How do I learn exploit API development?

I've been trying to learn how to make an Exploit API for a while now. Can anyone tell where I could start, where I will end, when I'll finally suceed, if anyone's willing to teach me perhaps? I legit don't wanna steal other's code or skid or use some form of a scummy shortcut, I wanna learn and make my own even if it takes time. Any form of help is much appreciated.