Thank you for the feedback!
I've added the tutorial screens in the last minutes, so they might be a little unclear on that. I'm gonna have to improve them to provide a better explanation. I'm also thinking about adding some sort of marker in the game itself, like maybe an arrow on the right side of your hand to point out that "the cards are played from here".
As for the expansion, I already have some ideas I had to remove because of the limited time. I wanted to have cards that would buff other cards in your hand (e. g. "reduce the mana cost of next card by 2" or "increase your next two attacks power by 1") and cards that change the order of following cards (e. g. "swap positions of the next two cards"). I also wanted to add minions in some form (e. g. minions played stay on the board and deal damage every turn until killed; enemy attacks target minions first before going back to the player), but I didn't manage to figure out a good (and fast!) way to do it.
Anyway, I've got some ideas for future updates. Not to mention all the improvements I didn't have time to do when it comes to the interface. Or adding things like sounds and music.