Learning about microcontrollers is like learning about anything complex.
You have to start by learning very simple things. Then you have to learn more complex things that build on your knowledge.
It will take time to learn these things.
If your goal is to learn about digital electronics, I would suggest that you start by learning about basic electronics, then Boolean Logic, then about Logic Gates, then Flip Flops and how to use these to construct state machines. Then learn about other logic ICs like counters, adders, multiplexers and demultiplexers.
You can then build on this knowledge to learn about microcontrollers, and how to connect them to circuits. You'll need to first learn about programming in a language like BASIC or C. You'll need to learn how to set up a circuit to connect to the microcontroller so you can program it.
Then you'll need to learn about different circuits that you can connect to the microcontroller, and how to use them. For example: learn how to read a switch value, learn how to light up an LED. Learn how to drive a piezo buzzer. Then learn how to drive a motor or use a regular speaker, using extra circuitry.
Michael