Forget all the documentation and books for now, the easist way, at least for me was to do something pratical.
To do something practical you ideally start with something that is fully functional or at least mostly functional and then you invent a feature and implement it.
The bad news is, Torque3D is not very functional by default, a lot of code has been removed in order to make Torque3D a more general game engine, where you have to do everything yourself, this may work for people who are already good at programming, but it will block off most people who don't (like me).
Developing a game takes a lot of time, so you have to work goal oriented and the goal is to get your feature done and save time, because your time is limited.
So what you should do now is, first think about what you want to do, like what kind of game you want to develop and then think what features you need to add, that do not already exist in Torque and then work them off one by one, starting with the easier ones and most importantly, don't try to code it yourself, but search first on the forum, especially the old garagegames forums if not already someone had the same idea/problem and maybe already solved it or at least tried to solve it, then you can look how that person did it and build upon it. Of course keep the documentation at hand with the basics, like the script syntax etc so you know what you can use in script.