I'll just give a quick breakdown from what I picked up today
You have two stats on each card, attack and damage. You have 12 life points and 12 barrels. Barrels are basically an attack multiplier.
You have four rounds, and each round you and your opponent pick a card, out of 4 randomly selected from your deck.
If you go first, you just do whatever. If you go second, you can see what card your opponent is playing, but not their barrels spent.
Once you've picked your card and added your barrels, whichever of the two cards, yours and your opponents, has the higher attack wins the round. Then, the damage total is removed from your life points.
Repeat until someone's life points reach zero or four rounds are ran. If the latter happens, whomever has the lowest life left loses. If it's a tie, then whomever went first in round 1 wins.