Download the full package of my e-book abou scripting. There's an English enhanced RMXP help file which can be pretty useful. It has all methods, definitions, properties and so on from built-in classes. If you wanna know about the classes in the scripts, simply read the comments in the code. Basically 1 slot if for one class. Sometimes more than 1 slot is for 1 class (like Game_Character, Scene_Battle, etc.)