Simple answer is: google for basic electronics youtube videos - for example "op-amps 101" or "op-amps basics". This gives you understanding of basic building blocks of electronics and then you may try to put those blocks together to form a more complex devices.
And - don't forget about basics of basics - Ohm's Law, Voltage and Current Laws, voltage dividers, how inductors and capacitors works, resonant circuits, diodes, transistors. Everyone of those topics was covered many times in some youtube videos.
Treat those videos as if they were lectures at school and make notes. I think this is one of the best way for self-learning electronics.