Ride your trialbike and jump over as many obstacles as you can. The more spectacular your stunts are, the more points you earn. Some stunts can be really difficult: the 360 degrees flip for example, requires good skills.
Use the up arrow to lean back, the down arrow to reverse, the right arrow to lean forward and the left arrow to lean back. Press A to use a nitro, S to break hard and D to jump. If you press R, you start from the last checkpoint. Combine keys to do special stunts: combine the left and up arrow to do a rear wheelie. Use the up arrow together with S and the right arrow to do a front wheelie. The up arrow, used together with the left arrow and D, guarantees a spectacular off ramp jump. You can do this same jump with an extra 360 degrees flip by pressing the left arrow an extra time.