The question is not about how to use "this, that, it" with material objects, but how to use them with non-material ones? I don't understand (it, that, this) yet.
I go to a gym every day and I like (it, this, that?).
You helped me and (it, this, that) is very good.
Is there any rule about (again it, this, that?)?
Suggestions? Can I use "this, that, it" interchangeably in most situations?