I'm sure that you will get a wide range of opinions about how to get started so look at each and decide what might make sense for you given your background, etc.
For me, after looking at examples in the Users Guide, Libraary, etc. I found that initially I was able to do simple things but ater awhile found it was more difficult to progress further. A friend suggested picking up some basic C++ knowledge with a "how to do it" book. On the forum others indicated that they found Bandy's books helpful. I looked into both routes and decided to go down the C++ road given the state of my AFL knowledge and prior limited exposure (a long time ago) to other languages.
So, about seven years ago, I looked around and found that short online "do it yourself" C++ courses were offered using books such as "C++ DeMystified" by Kent. I did not sign up for these courses but found that I could easily work through the Kent book fairly rapidly. The book also contains quizes at each step which I found quite useful in driving home key points that i might have overlooked.
To be sure, AFL is not C++ but it is not too far removed and is actually, imo, easier. Kent's book, however, gave me a good grounding in a variety of concepts, including functions, variables, loops (if-else, while-do), arrays, algorithms, etc. Armed with that I found that I could much more easily use the Users Guide or others code to figure out what I needed without or at most minimal assistance from others.
The route that I took is certainly not the only one but it did work for me. So, look around and dive in and whatever you decide will undoubtedly advance your coding skill.
Good luck and good trading.