Basically, what it does is, it lets you enable up to 5 people to use your Steam library when you're not using it. This means any game you own, except games that need a code or something in the game itself.
It does have limitations. While you're playing a game from your library, noone else can. But, if you're shared with someone, and they're shared with you, you can play games from each others libraries at the same time
Another thing to note: if two or more people are sharing games with you, and they have the same game that you don't, you'll only be able to play it from one of their libraries. Won't even see it from the other person. I think it depends on who shared first. So let the less active person share last
So, how to share. You need to log into your account on the other persons computer. If you're not at their computer, and don't trust them with your password, use teamviewer
In steam, go to settings, then family, and enable family sharing. Be sure to click "authorise this computer" and tick the name of the account you're sharing with. Log back into their account and you should see your games in their library
You will have to do this for every new computer, sadly. But it's a really cool way to play your friends games for free
