I read through a chunk of Lamport’s book and the first 7 or so sections of his online course (the rest weren’t posted yet).

https://lamport.azurewebsites.net/tla/tla.html

https://learntla.com/introduction/

Is also a good introduction. That was enough to make me dangerous. Since work didn’t have an interest in training me, and I had other obligations, that’s all I’ve done so far.

hwayne, who did learntla.com, is getting close to finishing a book on it. You could start with his online tutorial but get the book soon as it's out. Here's his Twitter in case you want to watch for the book release:

https://mobile.twitter.com/Hillelogram