The goal is to get points by inflating little balloons as big as you can, while staying inside the polygon. You have four balloons. The later ones score more points for the same size. I find it interestingly hard to try to spatially plan ahead to leave the most room for the blue one. Balloons 'pop' if they hit the edges of the polygon, but not if they hit other balloons.
(My best score so far is 2394.)