Go through the veils of proliferation and multiply your clones. Don't crash into obstacles, destroy your enemies with your clones. Reach enough clones for the bridge. Choose the weak barrel and make a way for yourself to progress. Try to reach the final with the most clones.
This game was clearly rushed, not only do you not have a use for the gems, but you can play about ten levels of this game and you already experienced everything it has to offer because this game recycles level designs a lot and it becomes really boring to play after that.