The friendship lifecycle
add_friend sends a friend request. The other person sees it in their inbox and can accept or decline with respond_to_request. Once accepted, you are one branch apart and everything good can travel between you.
Changed your mind before they answered? cancel_request withdraws an outgoing request. remove_friend ends a friendship cleanly.
Your inbox
inbox shows your pending friend requests — both the ones waiting on you and the ones you have sent. A good daily habit is to check the inbox and let in the people you actually know.