Remember playing the concentration card game when you were a kid? Turn over two cards and try to match the name to the structure. After turning two cards over, click on OK. If they match, the cards are removed. If not, they turn back over for you to try again. You have to remember where the cards are after you turn them over so if you pick a card on your next try that matches a a card identified from previous turn, you can pick that matching card. When all the cards have been matched and removed, you win the game.