To create a REST API using the Express framework, you need to follow these steps:

1. Install Node.js and npm (Node Package Manager) if you haven't already.
2. Create a new directory for your project and navigate to it in the terminal/command prompt.
3. Run `npm init` to initialize a new Node.js project and fill out the prompts.
4. Install necessary dependencies: express, mongoose, body-parser, and dotenv by running:
```
npm install express mongoose body-parser dotenv
```

5. Create a `.env` file in the root of your project directory and add your MongoDB connection string:
```
MONGODB_URI=mongodb+srv://username:password@cluster.mongodb.net/your-db-name?retryWrites=true&w=majority
```

6. Create an `app.js` file in the root of your project directory and paste the following code to set up the server and connect to MongoDB:

```javascript
const express = require('express');
const bodyParser = require('body-parser');
const mongoose = require('mongoose');
const dotenv = require('dotenv');

dotenv.config();

const app = express();
app.use(bodyParser.json());

mongoose.connect(process.env.MONGODB_URI, {
  useNewUrlParser: true,
  useUnifiedTopology: true,
});

const noteSchema = new mongoose.Schema({
  title: String,
  content: String,
  timestamp: Date,
});

const Note = mongoose.model('Note', noteSchema);

// Routes go here

const PORT = process.env.PORT || 3000;
app.listen(PORT, () => console.log(`Server started on port ${PORT}`));
```

7. Now let's implement the CRUD operations as routes:

- Create a note:

```javascript
app.post('/notes', async (req, res) => {
  try {
    const note = new Note({
      title: req.body.title,
      content: req.body.content,
      timestamp: new Date(),
    });

    await note.save();
    res.status(201).json(note);
  } catch (error) {
    res.status(500).json({ message: 'Error creating note' });
  }
});
```

- Read all notes:

```javascript
app.get('/notes', async (req, res) => {
  try {
    const notes = await Note.find({});
    res.json(notes);
  } catch (error) {
    res.status(500).json({ message: 'Error fetching notes' });
  }
});
```

- Read a single note by ID:

```javascript
app.get('/notes/:id', async (req, res) => {
  try {
    const note = await Note.findById(req.params.id);

    if (!note) {
      return res.status(404).json({ message: 'Note not found' });
    }

    res.json(note);
  } catch (error) {
    res.status(500).json({ message: 'Error fetching note' });
  }
});
```

- Update a note by ID:

```javascript
app.put('/notes/:id', async (req, res) => {
  try {
    const note = await Note.findByIdAndUpdate(
      req.params.id,
      {
        title: req.body.title,
        content: req.body.content,
        timestamp: new Date(),
      },
      { new: true }
    );

    if (!note) {
      return res.status(404).json({ message: 'Note not found' });
    }

    res.json(note);
  } catch (error) {
    res.status(500).json({ message: 'Error updating note' });
  }
});
```

- Delete a note by ID:

```javascript
app.delete('/notes/:id', async (req, res) => {
  try {
    const note = await Note.findByIdAndDelete(req.params.id);

    if (!note) {
      return res.status(404).json({ message: 'Note not found' });
    }

    res.json({ message: 'Note deleted successfully' });
  } catch (error) {
    res.status(500).json({ message: 'Error deleting note' });
  }
});
```

8. Save the `app.js` file and start your server by running `node app.js`. Your REST API should now be functional, allowing you to create, read, update, and delete notes using tools like Postman or CURL.

Remember that this is a basic implementation of a REST API with Express and MongoDB. In a production environment, you would want to add validation, authentication, and other security measures.
Express 프레임워크를 사용하여 REST API를 생성하려면 다음 단계를 따라야 합니다.

1. 아직 설치하지 않은 경우 Node.js 및 npm(Node 패키지 관리자)을 설치합니다.
2. 프로젝트의 새 디렉토리를 생성하고 터미널/명령 프롬프트에서 해당 디렉토리로 이동합니다.
3. npm init`을 실행하여 새 Node.js 프로젝트를 초기화하고 프롬프트를 작성합니다.
4. 실행하여 필요한 종속성(express, mongoose, body-parser, dotenv)을 설치합니다:
```
npm install express mongoose body-parser dotenv
```

5. 프로젝트 디렉터리 루트에 `.env` 파일을 생성하고 MongoDB 연결 문자열을 추가합니다:
```
MONGODB_URI=mongodb+srv://username:password@cluster.mongodb.net/your-db-name?retryWrites=true&w=majority
```

6. 프로젝트 디렉터리 루트에 `app.js` 파일을 생성하고 다음 코드를 붙여넣어 서버를 설정하고 MongoDB에 연결합니다:

```javascript
const express = require('express');
const bodyParser = require('body-parser');
const mongoose = require('mongoose');
const dotenv = require('dotenv');

dotenv.config();

const app = express();
app.use(bodyParser.json());

mongoose.connect(process.env.MONGODB_URI, {
  useNewUrlParser: true,
  useUnifiedTopology: true,
});

const noteSchema = new mongoose.Schema({
  title: String,
  content: String,
  timestamp: Date,
});

const Note = mongoose.model('Note', noteSchema);

// Routes go here

const PORT = process.env.PORT || 3000;
app.listen(PORT, () => console.log(`Server started on port ${PORT}`));
```

7. 이제 CRUD 작업을 경로로 구현해 봅시다.

- 노트를 만듭니다:

```javascript
app.post('/notes', async (req, res) => {
  try {
    const note = new Note({
      title: req.body.title,
      content: req.body.content,
      timestamp: new Date(),
    });

    await note.save();
    res.status(201).json(note);
  } catch (error) {
    res.status(500).json({ message: 'Error creating note' });
  }
});
```

- 모든 노트를 읽어보세요:

```javascript
app.get('/notes', async (req, res) => {
  try {
    const notes = await Note.find({});
    res.json(notes);
  } catch (error) {
    res.status(500).json({ message: 'Error fetching notes' });
  }
});
```

- ID로 하나의 노트를 읽습니다:

```javascript
app.get('/notes/:id', async (req, res) => {
  try {
    const note = await Note.findById(req.params.id);

    if (!note) {
      return res.status(404).json({ message: 'Note not found' });
    }

    res.json(note);
  } catch (error) {
    res.status(500).json({ message: 'Error fetching note' });
  }
});
```

- ID로 노트를 업데이트합니다:

```javascript
app.put('/notes/:id', async (req, res) => {
  try {
    const note = await Note.findByIdAndUpdate(
      req.params.id,
      {
        title: req.body.title,
        content: req.body.content,
        timestamp: new Date(),
      },
      { new: true }
    );

    if (!note) {
      return res.status(404).json({ message: 'Note not found' });
    }

    res.json(note);
  } catch (error) {
    res.status(500).json({ message: 'Error updating note' });
  }
});
```

- ID로 노트를 삭제합니다:

```javascript
app.delete('/notes/:id', async (req, res) => {
  try {
    const note = await Note.findByIdAndDelete(req.params.id);

    if (!note) {
      return res.status(404).json({ message: 'Note not found' });
    }

    res.json({ message: 'Note deleted successfully' });
  } catch (error) {
    res.status(500).json({ message: 'Error deleting note' });
  }
});
```

8. `app.js` 파일을 저장하고 `node app.js`를 실행해 서버를 시작합니다. 이제 REST API가 작동하여 Postman이나 CURL과 같은 도구를 사용해 노트를 만들고, 읽고, 업데이트하고, 삭제할 수 있을 것입니다.

이것은 Express와 MongoDB를 사용한 REST API의 기본 구현이라는 점을 기억하세요. 프로덕션 환경에서는 유효성 검사, 인증, 기타 보안 조치를 추가하고 싶을 것입니다.