Thanks for playing!
After crashing into a castle or running into edge, you can reverse the time (the default key is 'b') or restart the game.
If you collect the four triangles fast enough, you win. (The first track has two goal times, one should be very easy, and the other one should be very hard.) Then you can go to another track in the menu. (Other tracks have different shapes, and also their goals are sometimes different than "collect all the triangles fast enough".)