two things:
1) the other guy was correct, upon winning, press NOTHING. Just wait, and you will advance.
2) That's really not true. I don't really know how to explain it, but the longer a card stays on the field, the more it generates advantage over time if it can attack back (this isn't true for DPS cards, but those exist to force your opponent to waste resources on them). The game actually does play pretty well, however making a custom deck seems out because its quite easy to break.
You generally want to play at a loss at first and make it back pretty easily. The NPC seems programed to throw out their premium cards early, which you can use removal cards to damage them for quite a lot and x3 points. Over all, I guess I'm not explaining it well, but the games fairly intuitive. force your opponent to use the most resources to remove your cards while using the least amount to remove theirs. Eventually because all cards have to be played, knowing when to heal to stall and when to hold cards to damage multiple cards at once is kind of key.