Learn by doing
Sometimes the most effective way to learn something is to build it yourself. Though on its surface Git appears complicated, it's really based on a few simple ideas that can be realised with very little code in a high-level language. You can do it!
Work in small steps
Getting a working version control system off the ground can be done very quickly, and adding each new feature can be done a bit at a time. That means you can learn in small steps and work at your own pace.
It's not just about Git
Learning how Git works means you'll learn all sorts of other things in the process. Things like, what a cryptographic hash is, how to store trees efficiently, how diff and merge algorithms work, and a whole bunch of programming tricks.