First of all, that's not something you receive -- it's the Contacts and Friends page of your User Control Panel. "Your Notifications" displays a link to that page whenever there's been new activity that you should know about.

The contacts with "friendship requested" notations are ones to whom you've previously sent friend requests. If/when they accept your request, the gray square changes to a checkmark.

The incoming request(s) that you're being notified about will be at the bottom of that page. You check the ones you want to accept, then click "save" (or whatever that button says).