I'm an idiot so I don't understand what I'm doing, sorry

Sure, you don't build the deck, but there's  only a limited amount of cards that you pool from, which you can theoretically call a deck.

The goal of the game is to best your opponent by having a higher attack power than they do.

Some cards add attack bonuses every round.

It's a cute game, but I don't think the concept is a very strong one.