Open Steam
Go to Library
Right-click the game you want to share
Select Properties
Click the Local Files tab
Confirm the game is installed on this computer
On the computer where you want to play the shared game, open Steam
Sign in with your Steam account (the one you want to play from)
Go to Steam > Settings > Family
Enable Steam Family Sharing
Sign in with the account that owns the games
On the other computer (the one with the owned games), open Steam
Ensure Steam Family Sharing is enabled for the account you want to share with
On the library-sharing account, look under Library for the shared games
Click the shared game to start downloading/playing (if prompted)
If the game is not available, check that the game supports Family Sharing and that both accounts are authorized on the same Steam client