Q:

How to add options to the plugin page?

I can't find a more or less clear example on how to create additional fields, so may be someone can help me here? Here is my code:
function __construct(){
    add_action('admin_init', array($this, 'plugin_admin_init'));
}

public function create_fields(){
    register_setting('dleToWp_options', 'database_name');
    register_setting('dleToWp_options', 'database_prefix');
    register_setting('dleToWp_options', 'version');
    //Stuck here
    // add_settings_section('dleToWp_options', __('Settings', 'dleToWp'), NULL, 'dleToWp');
    // add_settings_field('plugin_text_string', 'Plugin Text Input', 'plugin_setting_string', 'plugin', 'dleToWp');
}

public function settings_page(){

    echo '<div class="wrap">
        <div class="icon32" id="icon-tools"></div>
        <h2>'.__('Database converter', 'dleToWp').'</h2>
        <form action="options.php" method="post">';
    settings_fields('dleToWp_options');
    do_settings_sections('dleToWp');
    echo '</form></div>';
}

I nee create 3 fields: Database name, database prefix and select box of versions.

A:

There are a lot of things which you have to understand about Settings API. Instead of duplicating information, I would strongly recommend you to read through bunch of articles called The Complete Guide To The WordPress Settings API, especially pay attention to the second part called Sections, Fields, and Settings. Don't hesitate to implement examples in articles, it will help you to understand and remember it better.

