If the game freezes, just click inside it (games can get unresponsive if you click elsewhere on the page).
The goal of the game is to get as many points in 90 seconds as possible. You swap Nyan Cats to form horizontal or vertical sets of the same color. The more Nyan Cats you can connect this way, the higher your score will be. Furthermore there are special stones as a reward if you can connect more then 3 Nyan Cats.