Pilot your ship by clicking in the world. The rocket will accelerate towards the mouse, burning fuel as it does so. Scroll to zoom the view. Test it out by clicking in the frame on the right.
To this end, you'll want to make use of the beauty of orbital mechanics. By flying close (not too close mind you) to a planet, you'll enter into its sphere of gravitational influence. Do this just right, and you'll be able to "slingshot" your craft, achieving a substantially higher exit than entrance velocity, while gaining "deltaV" (the change in velocity).