There are 3 rules when it comes to building a Gummi ship.
1: Your Gummi Ship must have a cockpit.
2: Your Gummi Ship must have at least 1 engine.
3: The engines of your Gummi Ship must be facing the correct way.
That's all there is to it. When you are at the Worlds Screen press the Square Button to go into the Gummi Garage. Chip and Dale will tell you a tutorial on how to do things. Read it and try to remember as much of it as you can. Then when it's over select Garage and then either pick a pre-made Blueprint. Or pick a fresh new one. Now you will be at a screen where you can see the Gummi Ship close up with a blue background. Now read below for the controls to use in this area. Trust me, trying to figure this out on your own is a pain in the butt. There are 3 different modes here. Select Mode is when you have a Gummi Block highlighted and you can switch between other Gummies. Build Mode is when you have chosen a Gummi Block and it is on the screen ready to be placed on the ship. Inspect Mode is when you have completed your ship and you would like a better look at, look at its status and see if it is flyable.