Yes. The game is completely free, with no ads and nothing to unlock. Tipping is optional and changes nothing in the game.
No. You can open a room and start playing right away. An account only matters if you want your match history, stats and leaderboard place to be saved.
Tap "Get started" to open a room, then send your friend the invite link. If it is easier to say it out loud, read them the room code and have them use "Join with code".
"Random match" puts you in the queue and pairs you with the next available player, usually within seconds.
A match runs to 3 or 5 round wins depending on the room. Both picks stay hidden until both players have locked in, and the server decides every round, so neither side can see the other choice early.