Gather small stars that match the color of your star. The color of your star will cycle through the spectrum so be careful, because the wrong color will shrink your star, shrink too much and the game ends.
EDIT: I should have explained this earlier. This game does have sound, but the volume starts at zero (change it in options,) so that it wouldn't annoy people if they wanted to put it on a myspace page or something with a music player already going. Just right click and select "Put this game on your site." and copy and paste the HTML.