There are lots of books and videos. You can even take electrical engineering classes.
But the best - and most fun - way to learn is hands-on.
I highly recommend building a CMoy. As you build it, read up on how the circuit functions and what each part does. You'll learn a lot and it'll get reinforced by building. You'll learn more and understand it more. Plus you'll have a cool little amp to use.

After that, you can build more powerful amps, preamps, power amps, phonostages, a DAC, a pair of speakers, tube gear, even a turntable and electrostatic headphones. You'll be able to fix everything yourself. Plus you'll get a deep understanding of what works and what doesn't and what stuff
really costs.
Don't get overwhelmed at first, though. Build a CMoy and see where that takes you.