You SELECT the buttons to the right of the File Type scrolling list to create and delete File Type entries, and to move them to and from a clipboard, as follows:
New creates a new File Type entry. The name of the first new entry is unnamed_1. If you create another new entry without renaming the first, it is called unnamed_2, etc.
To change the name of a File Type entry, type a new name in the Pattern text field and press Return. If you want to identify a set of files by a pattern, you must type the actual pattern in the Pattern text field. If you want to identify a set of files by content, the name of the File Type entry can be anything.
Cut removes the currently selected File Type entry from the current Binder entry (the entry selected in the base window scrolling list), and to move it to the clipboard. If the current Binder entry is a read-only entry, the Cut button is inactive.
Copy copies the currently selected File Type entry to the clipboard.
Paste adds the File Type entry that is on the clipboard to the current Binder entry. The Paste button is inactive if there is nothing on the clipboard.
Delete removes the File Type entry from the current Binder entry. The Delete button is inactive if the current Binder entry is a read-only entry. Note that deleting a Binder entry does not delete its File Type entry.
You use the Apply and Reset buttons at the bottom of the File Type Properties window to apply your File Type and Icon Properties changes to the current Binder entry, or to reset all the changes you've made since the last Apply.