If you've got a Steam account, you can share the games in your Steam library with other people in your household. (You're essentially sharing your library with their personal computers.) The household members who use that computer while logged into their personal Steam account can play your games on any computer you authorize to share games with. You can do this to a maximum of 10 different computers.
This process will only work on the linked computer
This process will only work on the linked computer, so other people won't be able to use your games with their account on another machine. They have to be logged into one of the computers with which you're authorized to share games.
If two people try to play the same game, the account owner will be given priority and the player who is only sharing access to the game will be prompted to close the title. This means you won't be able to game share with anyone to play together via multiplayer.