Once a custom menu item has been created, WordPress will call the function associated with it when it gets visited. The assigned function's main purpose is to render a configuration page containing a form with all the options available to the user and to send the captured data back to WordPress for processing.
There are two main methods that can be used to render plugin configuration pages: straight HTML and the Settings API. This recipe explores the use of HTML to create a configuration panel, while a later recipe will show how to use the Settings API to prepare the page output.