What are some good resources to learn APIs?

I'm not a developer. I actually work in identity and access management, tokens, authentication, etc. The closest I come to this would be powershell.

Some aspects of my job overlap with developers though. It seems that more often than not, tech that I'm responsible for implementing and administrating like secrets management, privlidged access and even directories all leverage APIs.

What resources would the HN crowd recommend for this non-dev to learn all about APIs?