I can confirm that the beginning of WoW coding was pretty hard for me, too.
A really good tutorial-style way to learn is
this book by Whitehead and Roe .
As mentioned by SDPhantom, WoWPedia is a good resource to look up the API. I think there are also some hello-world-like tutorials.
You have already discovered the /framestack command in game which allows you to hover over every UI element and see details about it. Pressing CTRL while hovering brings up another handy window to explore the UI frames and how they are related.
When you want to see the code behind the Blizzard UI, you have to extract the code as described
here. But personally I find it more comfortable to keep a clone of
this GitHub repository up to date, which always contains the most recent code. In this code you then search for whatever frame names you encounter to find out what is going on.
Another important tool is the in-game /eventtrace command, to see what events are happening that you can listen to in your addon.
Happy coding!