At the side of every Display-Name and on every User-Page you have the buttons to send someone a friend-request, follow them (see also “What are bookmarks? Why can I “follow” other users?”) or block them.
In your account under “Friends” is also an input-field where you can search for people to add. Here you have a list of friends you have, requests you have sent out and requests that have been sent to you.
Under your account in the tab “Blocked users” is a list of people you have blocked and an input-field where you can search for people to add. Blocked users can’t send you any private messages and you won’t see their comments on Story-Pages and Story-Blocks. You will, however, still see their Story-Pages and Story-Blocks.