requests is where you can see if you have got any friend requests, group or event invitations. you can confirm or reject all the requests here.
when viewing a profile, click the "add as a friend" link under the profile picture of the person. a friend request will be sent to the person and if s/he accepts it, s/he will be listed on your friends list.
no, you can not cancel the request which you sent.
basically, we do not send any notifications when someone rejects someone’s friend request.
