Steam doesn't properly support sharing games still. You can share your entire library and if you aren't playing anything at all, your friend can play a game from your library. Which you could do already, you just had to give your friend your password. Currently me and my brother share a library just fine by having one of us set steam to offline mode and then we can all play at the same time. It's less useful than the old behaviour, but without sharing your password. Oh and you can save in the cloud and earn achievements personally for yourself. Excuse me while I vomit.
Useless.