Pick a card, any card. You're trying to find all of the pairs of balls by using the least number of attempts possible. Click on one card to view it and click on the one you think matches it. If you guess right the cards will stay face up. Guess wrong and they will turn over and wait for your next attempt.
Stay alert! When your second card is picked and it is not a match it will turn over in a hurry. Try to remember where all of the cards are and match them up.