Method is used to Register Sidebar in function.php.

To register a sidebar in WordPress using the functions.php file, follow these steps:

1. Open your functions.php file: This file is located in your theme's folder. You can access it through your hosting file manager or using an FTP client.

2. Add the following code to your functions.php file:

function my_custom_sidebar() {
    register_sidebar(
        array (
            'name' => __( 'Custom', 'your-theme-domain' ),
            'id' => 'custom-side-bar',
            'description' => __( 'Custom Sidebar', 'your-theme-domain' ),
            'before_widget' => '<div class="widget-content">',
            'after_widget' => "</div>",
            'before_title' => '<h3 class="widget-title">',
            'after_title' => '</h3>',
        )
    );
}
add_action( 'widgets_init', 'my_custom_sidebar' );

3. Save your changes: After adding the code, save your changes and close the functions.php file.

4. Go to your WordPress dashboard: Navigate to Appearance > Widgets. You should see your new sidebar listed there.

5. Add widgets to your new sidebar: Simply drag and drop the widgets you want to appear in your new sidebar.

Remember to replace 'your-theme-domain' with your actual theme's domain. This code creates a new sidebar with the name 'Custom', and you can customize it as you wish.