Learning electronics
It sounds like the concepts you want to learn are incredibly broad. I would suggest first finding a project that intrigues you, and learning what you need to do to complete that project. How comfortable you are with the skills needed for that project will determine how far you delve into any individual concept, which will help you identify where you could potentially improve.

For example, let's say you want to build a robot. If you have little experience with this, your best bet might be to buy something like an Arduino and a pre-assembled chassis with motor driver electronics. You would learn how to write code for the Arduino and connect it to the electronics, and when it's all done, you have a neat little robot. This would give you exposure to basic concepts like the mechanics of small robots, the electronics needed to control them, and the control system needed to command those electronics. 

After doing a project like that, you might find yourself saying "gee, I really want stronger motors" which would lead to research on different motors and types of motors as well as bulkier electronics to drive them. Or perhaps you'd find yourself saying "the Arduino was nice but I want to use a different custom system" and then you could research how the Arduino works and figure out how you might replace it with your own system.

The gist of this all is that my recommendation is to complete a project that will expose you to many different paths of learning you could take, then after you finish, choose a path to follow deeper.