Thanks to chris-marks for a complete and awesome walkthrough, go check it out if you have problems with any level:
A horrid earthquake has occurred at a distant planetoid called Theia. The impact was so strong that it created a giant crack, running from the core of the planetoid until its surface. Your race finds out that this catastrophe was caused by a monster who is eating Theia's Core! If he continues, the planet will explode, destroying all of your race. Nonetheless, Voly dares to take the risk of stopping the monster and his evil minions by the cost of his own life.
Your goal is to guide Voly towards the center of Theia. But beware, Voly is way too weak to attack the huge enemies; therefore you should avoid confronting them.