It looks like you want to modify a C++ engine without prior knowledge of C++.
If that's the case, you'll need to get a grasp on C++ first. This will probably take weeks of really hard work (or months without classes or a good book).
But tutorials won't cut it; you'll need a better resource. Try to search wikibooks for a good C++ programming one.
If you already know C++, great!
1 - The second thing to do is to define what you need that the engine can't do. Write down the names of the features, or descriptions. You really need to do this step, if you can't name and describe your needs you probably don't know exactly what you want; nor if the engine can do it or not.
2 - Then you should describe why the engine can't do what you want. You'll probably discover some could be done in the engine.
3 - If even after this there's still missing features or capabilities you can go ahead and edit the code for the engine. If you really gone through step 2, you'll probably know what code you need to edit.
Out of curiosity, could you tell us at least one thing Torque3D can't do that you need?