If someone is using games from your library, then you can't play at the same time. You cannot play any games simultaneously. You can authorise up to 5 accounts and 10 computers to access your Steam gaming library.
Now they can download and install games from your Steam library. Let your friend/ family member now log into their own account. On the same PC, after authorising it, log out of your Steam account. On your friend's (or family member's) PC, log in with your Steam account. Select Manage my account with Steam Guard security. On your own computer, go to the Steam settings menu. From there, it's a relatively straightforward process. To do this, you'll need access to the computer on which your friends and/ or family play, and you will have to share your Steam account credentials (username and password) on their machine. As the name suggests, with this feature you can share your library of Steam games with friends and family. One of Steam's many useful features is Family Sharing. Valve's PC game distribution platform Steam has been in the news lately for a lot of reasons, such as allowing (and the removing) paid mods from Skyrim, or for adding a slew of features such as an in-game frame rate counter.
