Don, I learned everything I know about Arduino by watching YouTube videos, reading tutorial websites, and reading *numerous* Arduino books -- repeatedly. Then I learned how to send commands from an Arduino to a TMCC loco by studying Professor Chaos's code and writing very small proof-of-concept sketches. Just getting an engine to toot its whistle was a huge milestone, and extremely satisfying.
I started by watching this series of tutorials (several times) by Jeremy Blum: https://www.youtube.com/watch?v=fCxzA9_kg6s I strongly suggest you start there. He also has a book which covers pretty much the same material.
From your last post, I can say this is likely going to take you a lot of time. I personally spent hundreds of hours learning and experimenting, and I enjoyed every minute of it. But if you're really only interested in getting to the goal, the reward is not going to be worth the effort. To an experienced Arduino programmer, especially someone who is already up to speed with the TMCC and Legacy protocols etc., what you are trying to do is a relatively trivial project -- probably less than a hundred lines of code (versus thousands of lines of code for my Legacy control project, so far.) But for a novice, it's a long haul and only makes sense if the joy is in the journey.
For beginner books, I recommend Programming Arduino by Simon Monk. It covers basic programming concepts as well as how to interface with various devices such as LEDs, sensors, motors, etc. There is a second "advanced" volume that contains more good information for beginners.
After you understand the basics, for more of a deep dive into Arduino programming (with little emphasis on electronics), I highly recommend Beginning C for Arduino by Jack Purdum.
Good luck, and keep us posted on your progress!
