There is not much you can buy. It's mainly looking at other ppl code and trying to understand what they're doing.
A good source to find examples for certain things is:
https://wowpedia.fandom.com/wiki/World_of_Warcraft_API
Another good way is to look at the blizzard code of the element you want to work with:
https://github.com/Gethe/wow-ui-source/
So, get a small addon, see how it works and change it a little bit
For Ace3 there are some examples available, too:
https://www.wowace.com/projects/ace3...options-tables