If you have played the well-known game aa, you already know the idea behind Pin Circle. A wheel spins in the middle of the screen and a stack of pins waits at the bottom. Fire the pins into the wheel one at a time. Every pin that sticks becomes part of the wheel, spinning along with it, and the next pin must not touch any of them.
Tap to launch the next pin. It flies straight up and sticks into the edge of the wheel. Wait for a gap between the pins already there before you fire. As levels go on, you have more pins to place, up to 100 on the hardest stages, and the wheel changes speed: sometimes it crawls, sometimes it races, and sometimes it suddenly switches direction. Both very slow and very fast spins have their own way of tricking you.