One addition to the explanation. You need to select Applications to get the + sign.
From System Preferences/Help:
You can assign your own keyboard shortcuts to menu commands in any OS X app or in the Finder. This may be useful if, for example, one of the “global” shortcuts, which works the same in most apps, is used by one app for a different purpose. In this case, you can assign it a different key combination.
You can create keyboard shortcuts only for existing menu commands. You can’t define keyboard shortcuts for general purpose tasks such as opening an app or switching between apps.
If you assign a keyboard shortcut that already exists for another command or another app, your new shortcut won’t work. Find the menu command that’s using it and reassign the keyboard shortcut for that item.
To remove a customized shortcut, click Delete (–).
If you want to return all the shortcuts to their original key combinations, click Restore Defaults.
Thanks. Perhaps I'm using the wrong nomenclature. In Mountain Lion (and Lion also, I believe), there is a Finder-like list of recenlty opened Applications, Documents and Servers that is available in the Apple menu (far left, Apple icon) as "Recent Items". It's only Finder-like in that it doesn't offer the many Finder list view and sort options, but is a quick way to launch a recent document.
I'd like to be able to go to this list with a key stroke shortcut instead of a mouse click.