This list shows all the file extensions on your computer. When you modify an extension from this list it will be put into the user customized list. All extensions listed here are the default settings Windows uses.
Right click for menu.
This list shows all user customized and user created extensions for you the current logged in user. This is what Windows will use for any extensions you create or customize.
Right click for menu
Clicking the edit menu will allow you to edit the various file extension properties.
Clicking the new extension menu will allow you to enter the new extension then open the edit window so you can set various properties.
Delete will allow you to remove the extension. If it is in user customized, the extension will revert to its default settings.
The compare menu will open the scan extension window and allow you to scan for new or deleted extenstions in the Registry.
Open with editor will allow you to add or remove programs from Explorers right click menu - Open With.