Question about Steam Deck

[Wooky63]

So, I'm thinking of getting one of these for my Grandson.
- If I own a Steam game on my PC that is Steam Deck compatible like Fallout 4 or Doom, can I just download it to a Steam Deck and play it or do I have to purchase it again?
- I'm guessing that two Steam Deck consoles can play together in multi-player games...?

[cSg|mc-Hotsauce]

You don't need to purchase it again, no.

As long as the game is supported on Steam OS. Some multi-player games don't support Steam OS at all and some have anti-cheats that don't support Steam OS.