Hi @bdoucette
You have asked a pretty generic question which cannot be answered via a simple answer. Basically there are 2 ways to create custom API. Configuration and Customization. For configuration you do not need much technical knowledge or developer access as everything is done through IFS applications. Main drawback among many others is that you cannot write custom methods for the configured APIs. Below help doc covers pretty much everything and if you want to learn more, then I suggest you enroll in an IFS Academy course that covers custom objects framework.
Configuration - Technical Documentation For IFS Cloud
On the other hand, Customization is more developer oriented and you would at least need IFS Base server knowledge in order to customize existing APIs. Below is the help doc related to IFS development and also there are IFS Academy courses available as well.
Development Guide - Technical Documentation For IFS Cloud
Good luck!