2
Arrows and Z to select a level in the screen after the tutorial.
The main gameplay is split into two phases: building and platforming. During the build phase, use arrows to move your current piece into the grid, and place the piece with the Z key. Once there's at least 1 gem, you can use X to end the build phase (provided the last piece still fits into the grid). Oh and A key to rotate your current piece.
After you've pressed X, the platforming phase starts, and you can only use the arrow keys. Watch out for destructible blocks, spikes, and ropes. Your goal is to get all the gems and reach the exit door. If you can do that, you have a chance of setting a high score.