Like the other user said, Dimbeak's
series is what got me into mapping. He shows how to set up J.A.C.K. and everything you need to get started.
Lymphoid's
series is very new and he's responded to my comments fairly quickly so he can give you some help if you don't get something he's explaining.
Then there's
this tutorial series by Chaos7040 that has a lot of helpful videos as well.
All of these have helped me learn the real rudimentary basics. I've found some good old fashioned trial and error to be really helpful too. The subreddit r/hammer can also help you out if you have questions.