It's just match 3 mahjong. You have 7 inventory spaces to hold tiles and hope you get a match. You get 10 coins for completing a level, or 30 of you watch an ad. Idk why it doesn't just give me 30 coins, since I paid to remove ads, but greedy app is greedy. I've found shuffling to be the best way to save coins and generally will get you more mileage than the other options. What I don't understand is why the prices for shuffling, etc, hikes up at level 355. It's really dumb.