Yeah, that's on us. As the one responsible for uploading for this game jam, I take responsibility for not writing a tutorial or something about the rools (since there are no tooltips in the game). Your goal is to make sure your opponent has no cards left, by defeating all of their creatures. You take a card from your hand (if you've got the dice for it), place it on the field. Then you can click the card on the field to get up a skill menu in the lower right corner. Click one of the skills, then an opponent card. It should lose health. The damage dealt depends on defense and strength, so you could deal 0 damage.
I hope this helps! In this version it is not possible to back out of a decision once you've pressed something.
Thank you for playing!