There should be tutorials in game.

I can write up a thing though if you'd like? The basic ruleset is that you both have five cards. You both take turns playing a card on a 3x3 grid. All the cards have a value on each side (for instance, a card might have a top value of 3, a bottom value of 5, a right value of 8, and a left value of 1. Or something). When you play a card next to another, if its value facing that card is higher than the one it's next to, you 'capture' that card (it turns your color). At the end of the game (when all 9 cards are played), whoever has the most in their color wins.

There's advanced rules that implement fancy tricks (allowing you to capture cards with higher values), but that's the base game.

If that's confusing I can give a better example.