cpctelera is full of examples. They are ranked from easy to advanced and highlight the different APIs provided.
Also, it’s pretty pure C… So all the tutorials on the internet are usable.
Obviously, knowing a bit of assembly is a plus. It’s easy to integrate directly into your project if you need to optimize certain parts.
I made my Minesweeper game with it; it’s right here if you want to check out the project: Roland goes Demining I have added the project sources inside a zip in the thread.