Before each level, drag parts from the Parts Window into the Assembly Window to put together your vehicle. All vehicles have an engine, body, and wheels. Later you'll get joints to hold parts together and weapons to fight bad guys. To move parts around the Assembly Window, click a part and then where you'd like to place it. Place tires so that their axis (center) is attached to the body. Place the engine inside the body. The blue buttons on the bottom left will allow you to start over with building and preview the track. When you're ready, click the green button to start the level. You pass the level if your vehicle makes it to the finish flag. Click the thumbs down button if you need to make some adjustments to your vehicle in the Assembly Window. If you get stuck on a level, look for hints!