1. Navigate to the WordPress plugin directory of your development installation.
2. Create a new directory called ch3-settings-api.
3. Navigate to this directory and create a new text file called ch3-settings-api.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 3 - Settings API.

5. Add the following line of code to register a function that will be called when WordPress activates the plugin:

register_activation_hook( __FILE__, 
                          'ch3sapi_set_default_options' );

6. Add the following code section to provide an implementation for the ch3sapi_set_default_options function to set default plugin options:

function ch3sapi_set_default_options() {
    ch3sapi_get_options();
}

7. Add the following code to provide an implementation for the ch3sapi_get_options function:

function ch3sapi_get_options() {
    $options = get_option( 'ch3sapi_options', array() );

    $new_options['ga_account_name'] = 'UA-0000000-0';
    $new_options['track_outgoing_links'] = false;

    $merged_options = wp_parse_args( $options, $new_options );

    $compare_options = array_diff_key( $new_options, $options );
    if ( empty( $options ) || !empty( $compare_options ) ) {
        update_option( 'ch3sapi_options', $merged_options );
    }
    return $merged_options;
}

8. Add the following registration function to associate a callback with the admin_init action hook:

add_action( 'admin_init', 'ch3sapi_admin_init' );

9. Add an implementation for the ch3sapi_admin_init function, creating the settings group for the plugin and defining its contents:

function ch3sapi_admin_init() {
    // Register a setting group with a validation function
    // so that post data handling is done automatically for us 
    register_setting( 'ch3sapi_settings',
        'ch3sapi_options', 'ch3sapi_validate_options' );
 
    // Add a new settings section within the group
    add_settings_section( 'ch3sapi_main_section', 'Main Settings',
        'ch3sapi_main_setting_section_callback',
        'ch3sapi_settings_section' );
 
    // Add each field with its name and function to use for
    // our new settings, put them in our new section 
    add_settings_field( 'ga_account_name', 'Account Name',
        'ch3sapi_display_text_field', 'ch3sapi_settings_section',
        'ch3sapi_main_section',
        array( 'name' => 'ga_account_name' ) );
 
    add_settings_field( 'track_outgoing_links',
        'Track Outgoing Links', 'ch3sapi_display_check_box',
        'ch3sapi_settings_section', 'ch3sapi_main_section',
        array( 'name' => 'track_outgoing_links' ) );
}

10. Declare a body for the ch3sapi_validate_options function, which was declared when registering the settings in the previous section:

function ch3sapi_validate_options( $input ) {
    foreach ( array( 'ga_account_name' ) as $option_name ) { 
        if ( isset( $input[$option_name] ) ) { 
            $input[$option_name] = 
                sanitize_text_field( $input[$option_name] ); 
        } 
    } 
 
    foreach ( array( 'track_outgoing_links' ) as $option_name ) { 
        if ( isset( $input[$option_name] ) ) { 
            $input[$option_name] = true; 
        } else { 
            $input[$option_name] = false; 
        } 
    }
    return $input;  
}

11. Declare a body for the ch3sapi_main_setting_section_callback function, declared when the settings section was created:

function ch3sapi_main_setting_section_callback() { ?>
    <p>This is the main configuration section.</p>
<?php }

12. Provide an implementation for the ch3sapi_display_text_field function, declared when a text field was added to the settings section:

function ch3sapi_display_text_field( $data = array() ) {
    extract( $data );
    $options = ch3sapi_get_options();
    ?>
    <input type="text" name="ch3sapi_options[<?php echo $name; ?>]"
           value="<?php echo esc_html( $options[$name] ); ?>"/>
    <br />
<?php }

13. Declare and define the ch3sapi_display_check_box function, declared when a checkbox was added to the settings section:

function ch3sapi_display_check_box( $data = array() ) {
    extract ( $data );
    $options = ch3sapi_get_options();
    ?>
    <input type="checkbox" 
           name="ch3sapi_options[<?php echo $name;  ?>]"
           <?php checked( $options[$name] ); ?>/>
<?php }

14. Add the following line of code to register a function that will be called when WordPress is preparing data to display the site's administration menu:

add_action( 'admin_menu', 'ch3sapi_settings_menu' );

15. Provide code for the implementation of the ch3sapi_settings_menu function:

function ch3sapi_settings_menu() {
    add_options_page( 'My Google Analytics Configuration',
        'My Google Analytics - Settings API', 'manage_options',
        'ch3sapi-my-google-analytics', 'ch3sapi_config_page' );
}

16. Add a definition for the ch3sapi_config_page function, defined when the new options page was declared:

function ch3sapi_config_page() { ?>
    <div id="ch3sapi-general" class="wrap">
    <h2>My Google Analytics - Settings API</h2>
 
    <form name="ch3sapi_options_form_settings_api" method="post"
          action="options.php">
 
    <?php settings_fields( 'ch3sapi_settings' ); ?>
    <?php do_settings_sections( 'ch3sapi_settings_section' ); ?>
 
    <input type="submit" value="Submit" class="button-primary" />
    </form></div>
<?php }

17. Save and close the plugin file.
18. Navigate to the Plugins menu of the administration area.
19. Activate your new plugin.
20. Navigate to the Settings menu and click on the My Google Analytics - Settings API menu item to see the configuration page for this plugin.

21. Make a change to the options and submit them to see that they are automatically handled by WordPress without having written express code to save options.