To create a simple blog application using Flask, we'll first need to install the required packages. You can do this by running:

```bash
pip install flask flask-sqlalchemy flask-login
```

Now let's start building our application step-by-step.

1. Create a new file called `app.py` and add the following code to set up the basic structure of the Flask app:

```python
from flask import Flask

app = Flask(__name__)

@app.route('/')
def home():
    return 'Hello, World!'

if __name__ == '__main__':
    app.run(debug=True)
```

2. Set up the database configuration and initialize SQLAlchemy:

```python
# Add these imports at the top of your app.py file
from flask_sqlalchemy import SQLAlchemy
from flask_login import LoginManager

# Configure the database URI and initialize SQLAlchemy
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///blog.db'
db = SQLAlchemy(app)

# Initialize the login manager
login_manager = LoginManager()
login_manager.init_app(app)
```

3. Define the User, Post, and Comment models for the database:

```python
from datetime import datetime

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(80), unique=True, nullable=False)
    email = db.Column(db.String(120), unique=True, nullable=False)
    password = db.Column(db.String(128), nullable=False)
    posts = db.relationship('Post', backref='author', lazy=True)
    comments = db.relationship('Comment', backref='author', lazy=True)

class Post(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    title = db.Column(db.String(200), nullable=False)
    content = db.Column(db.Text, nullable=False)
    date_posted = db.Column(db.DateTime, nullable=False, default=datetime.utcnow)
    user_id = db.Column(db.Integer, db.ForeignKey('user.id'), nullable=False)
    comments = db.relationship('Comment', backref='post', lazy=True)

class Comment(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    content = db.Column(db.Text, nullable=False)
    date_posted = db.Column(db.DateTime, nullable=False, default=datetime.utcnow)
    user_id = db.Column(db.Integer, db.ForeignKey('user.id'), nullable=False)
    post_id = db.Column(db.Integer, db.ForeignKey('post.id'), nullable=False)
```

4. Create the database tables by running the following commands in your terminal:

```bash
python
from app import db
db.create_all()
exit()
```

5. Set up user authentication using Flask-Login:

```python
# Add this import at the top of your app.py file
from flask_login import UserMixin

# Modify the User class to inherit from UserMixin
class User(UserMixin, db.Model):
    # ...

@login_manager.user_loader
def load_user(user_id):
    return User.query.get(int(user_id))
```

6. Implement routes for user registration, login, and logout:

```python
from flask import render_template, url_for, flash, redirect, request
from werkzeug.security import generate_password_hash, check_password_hash
from flask_login import login_user, current_user, logout_user, login_required

@app.route('/register', methods=['GET', 'POST'])
def register():
    if current_user.is_authenticated:
        return redirect(url_for('home'))
    if request.method == 'POST':
        username = request.form['username']
        email = request.form['email']
        password = request.form['password']
        hashed_password = generate_password_hash(password)
        user = User(username=username, email=email, password=hashed_password)
        db.session.add(user)
        db.session.commit()
        flash('Your account has been created! You can now log in.', 'success')
        return redirect(url_for('login'))
    return render_template('register.html')

@app.route('/login', methods=['GET', 'POST'])
def login():
    if current_user.is_authenticated:
        return redirect(url_for('home'))
    if request.method == 'POST':
        email = request.form['email']
        password = request.form['password']
        user = User.query.filter_by(email=email).first()
        if user and check_password_hash(user.password, password):
            login_user(user)
            next_page = request.args.get('next')
            return redirect(next_page) if next_page else redirect(url_for('home'))
        else:
            flash('Login unsuccessful. Please check your email and password.', 'danger')
    return render_template('login.html')

@app.route('/logout')
def logout():
    logout_user()
    return redirect(url_for('home'))
```

7. Implement routes for creating, viewing, and deleting posts:

```python
@app.route('/post/new', methods=['GET', 'POST'])
@login_required
def create_post():
    if request.method == 'POST':
        title = request.form['title']
        content = request.form['content']
        post = Post(title=title, content=content, author=current_user)
        db.session.add(post)
        db.session.commit()
        flash('Your post has been created!', 'success')
        return redirect(url_for('home'))
    return render_template('create_post.html')

@app.route('/post/<int:post_id>')
def view_post(post_id):
    post = Post.query.get_or_404(post_id)
    comments = Comment.query.filter_by(post_id=post_id).all()
    return render_template('view_post.html', post=post, comments=comments)

@app.route('/post/<int:post_id>/delete', methods=['POST'])
@login_required
def delete_post(post_id):
    post = Post.query.get_or_404(post_id)
    if post.author != current_user:
        abort(403)
    db.session.delete(post)
    db.session.commit()
    flash('Your post has been deleted!', 'success')
    return redirect(url_for('home'))
```

8. Implement routes for creating and deleting comments:

```python
@app.route('/post/<int:post_id>/comment', methods=['POST'])
@login_required
def create_comment(post_id):
    content = request.form['content']
    comment = Comment(content=content, author=current_user, post_id=post_id)
    db.session.add(comment)
    db.session.commit()
    flash('Your comment has been posted!', 'success')
    return redirect(url_for('view_post', post_id=post_id))

@app.route('/comment/<int:comment_id>/delete', methods=['POST'])
@login_required
def delete_comment(comment_id):
    comment = Comment.query.get_or_404(comment_id)
    if comment.author != current_user:
        abort(403)
    post_id = comment.post_id
    db.session.delete(comment)
    db.session.commit()
    flash('Your comment has been deleted!', 'success')
    return redirect(url_for('view_post', post_id=post_id))
```

9. Create the necessary HTML templates (`base.html`, `register.html`, `login.html`, `create_post.html`, `view_post.html`) in a folder named `templates`. You can find examples of these templates in the Flask documentation or various online tutorials.

10. Run your application by running `python app.py` in your terminal.

This is just a basic implementation of a blog application using Flask, SQLAlchemy, and Flask-Login. There are many improvements that could be made, such as adding error handling, form validation, pagination, and more. However, this should give you a good starting point for building your own blog application.
Flask를 사용하여 간단한 블로그 애플리케이션을 만들려면 먼저 필요한 패키지를 설치해야 합니다. 실행하면 됩니다:

```bash
pip install flask flask-sqlalchemy flask-login
```

이제 애플리케이션을 단계별로 빌드해 보겠습니다.

1. `app.py`라는 새 파일을 생성하고 다음 코드를 추가하여 플라스크 앱의 기본 구조를 설정합니다:

```python
from flask import Flask

app = Flask(__name__)

@app.route('/')
def home():
    return 'Hello, World!'

if __name__ == '__main__':
    app.run(debug=True)
```

2. 데이터베이스 구성을 설정하고 SQLAlchemy를 초기화합니다:

```python
# Add these imports at the top of your app.py file
from flask_sqlalchemy import SQLAlchemy
from flask_login import LoginManager

# Configure the database URI and initialize SQLAlchemy
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///blog.db'
db = SQLAlchemy(app)

# Initialize the login manager
login_manager = LoginManager()
login_manager.init_app(app)
```

3. 데이터베이스에 대한 사용자, 글, 댓글 모델을 정의합니다:

```python
from datetime import datetime

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(80), unique=True, nullable=False)
    email = db.Column(db.String(120), unique=True, nullable=False)
    password = db.Column(db.String(128), nullable=False)
    posts = db.relationship('Post', backref='author', lazy=True)
    comments = db.relationship('Comment', backref='author', lazy=True)

class Post(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    title = db.Column(db.String(200), nullable=False)
    content = db.Column(db.Text, nullable=False)
    date_posted = db.Column(db.DateTime, nullable=False, default=datetime.utcnow)
    user_id = db.Column(db.Integer, db.ForeignKey('user.id'), nullable=False)
    comments = db.relationship('Comment', backref='post', lazy=True)

class Comment(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    content = db.Column(db.Text, nullable=False)
    date_posted = db.Column(db.DateTime, nullable=False, default=datetime.utcnow)
    user_id = db.Column(db.Integer, db.ForeignKey('user.id'), nullable=False)
    post_id = db.Column(db.Integer, db.ForeignKey('post.id'), nullable=False)
```

4. 터미널에서 다음 명령을 실행하여 데이터베이스 테이블을 생성합니다:

```bash
python
from app import db
db.create_all()
exit()
```

5. 플라스크 로그인을 사용하여 사용자 인증을 설정합니다:

```python
# Add this import at the top of your app.py file
from flask_login import UserMixin

# Modify the User class to inherit from UserMixin
class User(UserMixin, db.Model):
    # ...

@login_manager.user_loader
def load_user(user_id):
    return User.query.get(int(user_id))
```

6. 사용자 등록, 로그인 및 로그아웃을 위한 경로를 구현합니다:

```python
from flask import render_template, url_for, flash, redirect, request
from werkzeug.security import generate_password_hash, check_password_hash
from flask_login import login_user, current_user, logout_user, login_required

@app.route('/register', methods=['GET', 'POST'])
def register():
    if current_user.is_authenticated:
        return redirect(url_for('home'))
    if request.method == 'POST':
        username = request.form['username']
        email = request.form['email']
        password = request.form['password']
        hashed_password = generate_password_hash(password)
        user = User(username=username, email=email, password=hashed_password)
        db.session.add(user)
        db.session.commit()
        flash('Your account has been created! You can now log in.', 'success')
        return redirect(url_for('login'))
    return render_template('register.html')

@app.route('/login', methods=['GET', 'POST'])
def login():
    if current_user.is_authenticated:
        return redirect(url_for('home'))
    if request.method == 'POST':
        email = request.form['email']
        password = request.form['password']
        user = User.query.filter_by(email=email).first()
        if user and check_password_hash(user.password, password):
            login_user(user)
            next_page = request.args.get('next')
            return redirect(next_page) if next_page else redirect(url_for('home'))
        else:
            flash('Login unsuccessful. Please check your email and password.', 'danger')
    return render_template('login.html')

@app.route('/logout')
def logout():
    logout_user()
    return redirect(url_for('home'))
```

7. 글을 작성하고, 보고, 삭제하는 경로를 구현합니다:

```python
@app.route('/post/new', methods=['GET', 'POST'])
@login_required
def create_post():
    if request.method == 'POST':
        title = request.form['title']
        content = request.form['content']
        post = Post(title=title, content=content, author=current_user)
        db.session.add(post)
        db.session.commit()
        flash('Your post has been created!', 'success')
        return redirect(url_for('home'))
    return render_template('create_post.html')

@app.route('/post/<int:post_id>')
def view_post(post_id):
    post = Post.query.get_or_404(post_id)
    comments = Comment.query.filter_by(post_id=post_id).all()
    return render_template('view_post.html', post=post, comments=comments)

@app.route('/post/<int:post_id>/delete', methods=['POST'])
@login_required
def delete_post(post_id):
    post = Post.query.get_or_404(post_id)
    if post.author != current_user:
        abort(403)
    db.session.delete(post)
    db.session.commit()
    flash('Your post has been deleted!', 'success')
    return redirect(url_for('home'))
```

8. 댓글을 작성하고 삭제하는 경로를 구현합니다:

```python
@app.route('/post/<int:post_id>/comment', methods=['POST'])
@login_required
def create_comment(post_id):
    content = request.form['content']
    comment = Comment(content=content, author=current_user, post_id=post_id)
    db.session.add(comment)
    db.session.commit()
    flash('Your comment has been posted!', 'success')
    return redirect(url_for('view_post', post_id=post_id))

@app.route('/comment/<int:comment_id>/delete', methods=['POST'])
@login_required
def delete_comment(comment_id):
    comment = Comment.query.get_or_404(comment_id)
    if comment.author != current_user:
        abort(403)
    post_id = comment.post_id
    db.session.delete(comment)
    db.session.commit()
    flash('Your comment has been deleted!', 'success')
    return redirect(url_for('view_post', post_id=post_id))
```

9. 템플릿`이라는 폴더에 필요한 HTML 템플릿(`base.html`, `register.html`, `login.html`, `create_post.html`, `view_post.html`)을 생성합니다. 이러한 템플릿의 예제는 Flask 설명서 또는 다양한 온라인 튜토리얼에서 찾을 수 있습니다.

10. 터미널에서 `python app.py`를 실행하여 애플리케이션을 실행합니다.

이것은 Flask, SQLAlchemy 및 Flask-Login을 사용하는 블로그 애플리케이션의 기본 구현에 불과합니다. 오류 처리, 양식 유효성 검사, 페이지 매김 등을 추가하는 등 개선할 수 있는 부분이 많이 있습니다. 그러나 이것은 여러분만의 블로그 애플리케이션을 구축하기 위한 좋은 출발점이 될 것입니다.