This page outlines what each of the files a truckmaker will be dealing with is and briefly describes what you need to do to edit them.
All about .BIN files.
All about .RAW, .PAL and .ACT files. These are all interlinked, so I put them all on one page.
How to decipher a .TRK file.
What .WAV files do in the game.
The .POD file.