1. Navigate to the WordPress plugin directory of your development installation.
2. Create a new directory called ch2-private-item-text.
3. Navigate to this directory and create a new text file called ch2-private-item-text.php.
4. Open the new file in a code editor and add an appropriate header at the top of the plugin file, naming the plugin Chapter 2 - Private Item Text.
5. Add the following line of code to declare a new shortcode and specify the name of the function that should be called when the shortcode is found in posts or pages:

add_shortcode( 'private', 'ch2pit_private_shortcode' ); 

6. Add the following code section to provide an implementation for the ch2pit_private_shortcode function:

function ch2pit_private_shortcode( $atts, $content = null ) { 
    if ( is_user_logged_in() ) {
        return '<div class="private">' . $content . '</div>'; 
    } else {
        $output = '<div class="register">';
        $output .= 'You need to become a member to access ';
        $output .= 'this content.</div>';
        return $output;
    }
} 

7. Save and close the plugin file.
8. Log in to the administration page of your development WordPress installation.
9. Click on Plugins in the left-hand navigation menu.
10. Activate your new plugin.
11. Create a new post and wrap some of the content with the [private] and [/private] tags:

12. Save and view the post to see that the text is visible while you are logged in to your site.
13. Log out and refresh the page to see that the enclosed text has been replaced by a general message.