Alright, I'm gonna take a crack at this. Note, I wasn't supposed to do this, since somebody who modified my first ship for me said he'd make this guide for me, but eh. I'll give it a try. After all, you know what they say, "If you want something done right, do it yourself." Or something.

OK, on the Worlds map, press square to go to the Gummi Garage. When there, you can read the tutorial ifya want, but it didn't really help me. Choose "Garage," then choose your blueprint (the one on my "super" game (my original game) is practically invincible now, what with my monkie-ing with it, and it's still only a modified Kingdom model).

Use the arrow keys to flick back and forth to see what gummis you have so far. To take stuff off yer gummi ship, press R1, move the arrow keys around til you find whatya wanna remove, then press O. Ifya wanna add a gummy, choose the gummi, then position it whereya want it to go (if the name goes bright green, that means you can put that there). Use the left analog stick to rotate the gummi to your liking, and the right one to rotate both the ship and the gummi piece. R1 lets you modify the ship, and L1 and L2 lower and raise the ship, respectively. When yer done, press O and hit Save and Yes, then Exit.

Also, you'll want to buy Sys Up 1, Sys Up 2, Com Lv 1, Com Lv 2, and Com Lv 3 from Cid as soon as possible. Sys Up expands your work area in the Gummi Garage, and Com Lv lets you add more gummi blocks to your ship.

Gepetto will give you blueprints for new gummi ships based on how many Heartless you kill (no, sorry, I don't know the numbers). Visit him every so often to get new ones. I'll make a table with the ships later. You can also get blueprints by defeating Heartless ships when yer flying in normal mode between worlds.