Keep tapping rounded squares with a number "10" as quickly as possible. You have 30 seconds to tap as many 10s as possible. The faster you tap, the more points you get. In case you tap another number, your result will be decreased by 15 points.
There are rounded squares with a number "10" and a yellow star in a top-right corner as well. If you tap them you get even more points! They are worth up to 100 points each, depending on how quickly you tap.
There are special dark green squares with a clock icon inside as well. If you tap them you earn 3 extra seconds to your game's time.