Ah, I see. So you have good practical skills at "mechanical" end of electronics and you want to buttress that with some more technical understanding.
I guess the best approach is for you to let us know where you're at already with understanding of basic components, circuits, etc., and then to choose a path to follow. Electronics is a very broad area of knowledge and it's perhaps best to get a general understanding of basic components and rules (if you don't have these already) before looking more deeply along a path that interests you.