To "friend" someone, just go to their "user info" page. The easiest way to go there is to click on the little human "head" next to someone's LJ name -- like the head next to the name "shirebound" on this message. Or go to your own "user info" page and type in the person's LJ name in the "search" box at the top of the page. Once you're at their page, you'll see a line of icons at the top. The first one is a little "head" with a plus-sign next to it. If you click this, then click "OK', you've friended someone, and their posts will show up on your "friends" page.