Hi :) In order to challenge a friend to a live game, you both need to be logged into live chess. Hope that helps!
In Live Chess, you can see your friends on the "Friends" tab. (They have to be connected to Live Chess; you won't see them here if they are using Tactics Trainer or other Chess.com features.)
On the Friends tab, you can click "Play" found next to your friends name, to challenge them (if it says "Watch" instead of "Play" it means they are already playing a game, which you can observe).
https://support.chess.com/customer/portal/articles/1444882
Hope that helps!
How can I challenge a friend to a live game? I went to friends and selected Challenge, but it only allowe Online Games.