Add custom functionality

- [Instructor] In this tutorial,…we're going to add some custom functionality to our plugin.…In previous videos, we added all the code necessary…to get the plugin to this point.…We've added the menu item, plugin page,…registered all settings, to find all callback functions,…and made some other optimizations…to make sure that everything is safe and secure.…So now we want to add the actual functionality…that will make this plugin do something…other than just remember settings.…For this plugin, we have a section of options…for the user to customize the login page,…and another set of options…for the user to customize the admin area.…

So now we want to add the functionality…for each of these seven features.…Let's do so, one at a time,…beginning with the Custom URL feature.…First, let's create a new file.…We're going to put this file in the includes folder.…I'm going to name it core-functions.php.…This file will be available to…all admin and public-facing pages,…as explained in the previous video,…creating the plugin directory and files.…