How in the heck do you allow other users on their own PCs to access your steam account (so I do not have to buy two copies of game)?

I have dug around steam settings and dug through the steam forum but nothing works.

I even created another account for my kid but I cannot add it to my family, really steam, wtf.

ETA: I think I have it working, I will know if it works once my kids are home. More to follow.
ETA2: Family sharing works, enable it under interface and steam family beta. One problem thought, I own poppy playtime chapters 1, 2, and 3 but my kid can only play chapter 1, steam says they must buy 2 and 3. wtf.

Unless I'm not understanding...both myself and my son have accounts on his PC, I can play his games, he can play mine.

I do share the account info with him, so that's probably why.

ETA: Yeah, create a user account on his PC, download your steam and games there and either let him use that account or
give him access to your steam.

I own poppy play time chapters 1, 2, and 3 but under my kids account, they can only play chapter 1, says they must buy chapters 2 and 3. Wtf.

Thanks, I gave my kid access to my account but see my problem above.