As one of the tests that the trio needed to pass to get to the room where Philosopher's Stone was kept, they needed to get across the room full of giant wizard chess.
To do that, they needed to play the game, which the book describes as seriously dangerous for them - the chess figures literally crush and destroy one another, and wreck things around.
What makes me confused is, how did Quirrell get past this test?
It seems unlikely that HE played wizard chess - first, given what's shown about the game, any prior recent game would have left mounds of debris and broken figures all over the place; and second, there were 3 missing figures and only one Quirrell.
If he used some other method to avoid playing the game, what was it, and why couldn't the trio use the same method instead of risking Ron's life?