Getting started with APIs

I have an API for my LMS (Learning Management System) and I'd like to integrate it with ZCRM. My only experience with APIs is here in Zoho. I've connected CRM with other Zoho apps, but all the work is done for you. I just copy and paste the provided key.

Can someone point me to a document or help file to newbies, please? I've scoured the internet. All of the info I have found make assumptions about the reader's knowledge of working with APIs. Any direction will be greatly appreciated.