You should have already followed the Accessing user settings from action and filter hooks recipe, and the resulting plugin should be active in your development site. Alternatively, you can get the resulting code (Chapter 3/ch2-page-header-output/ch2-page-header-output-v9.php) from the downloaded code bundle and rename the file ch2-page-header-output-v9.php as ch2-page-header-output.php before starting this recipe. You should also have access to a WordPress installation configured in Network mode. You can read more about the steps required to configure WordPress to run as a multisite at https://codex.wordpress.org/Create_A_Network.