I've got great news for you!
You're already there.
Just start reading these threads. Click on any headline that looks interesting and read until you've finished the thread or lost interest. Then click on another. You'll learn a lot quickly. You'll have a few laughs, too.
I suppose there are reference books and technical websites and such. But you'll need to find different ones for the different types of engines and motors, drivetrains and such. And it'll be dull reading.
You'll have a lot more fun here.