Leap from platform to platform to collect crystals -- just be sure not to fall in the lava.
Collect the crystal, then return to the outer rim of the level.
Use the UP arrow to leap towards the center of the screen, use the DOWN arrow to leap away from the center.
Time your jumps so you land on the platforms -- aim for the dead center of the platform for best results!
(If the game seems to be ignoring you, you may just need to click on it once at the beginning.)
Version 2.0 adds 5 new levels and also includes fireballs which you must avoid while jumping from platform to platform.