Maybe try out my vi quickstart tutorial:

https://gumroad.com/l/vi_quick/

vi is the predecessor of, and a subset of, vim, and is probably available on even more platforms than vim is. So knowledge of that single editor (vi) enables you to work on any of those platforms. And you can always progress to (and through - it is big) vim later, at your own pace.

I wrote it at the request of two Windows system administrator friends who were given additional charge of some Unix systems. They later told me that it helped them to quickly start using vi to edit text files on Unix.