Steam Support :: Family Library Sharing
https://help.steampowered.com/en/faqs/view/57A7-503C-991F-E9A8
Log into your Steam account on the computer where you'd like to share your games. Make sure that you have Steam Guard security enabled via Steam > Settings > Account in the Steam Client. From the Steam Settings panel select the Family tab (or in Big Picture mode, Settings > Family Library Sharing). ... Click the "Authorize Library Sharing on this Computer" box.
Log into your Steam account on the computer where you'd like to share your games.
Make sure that you have Steam Guard security enabled via Steam > Settings > Account in the Steam Client.
From the Steam Settings panel select the Family tab (or in Big Picture mode, Settings > Family Library Sharing). ...
Click the "Authorize Library Sharing on this Computer" box.
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