Consider I only know apis are structured data that can be called or modified from within a program, and have no real further knowledge in real use cases nor in networking.
Where should I start from? Should I study backend?
I prefer docs rather than videos.
It should be noted that theoretically, we don’t know how this external API is implemented. The vast majority of APIs are REST APIs and with REST APIs, there’s a decent chance that you can download an OpenAPI definition from the server which provides the API.
REST APIs are basically APIs which use HTTP(S) for transport and then there’s some specific rules how the API should be designed. Often times, these rules are not strictly followed and people still refer to such an API as “REST”, because they assume that any HTTP API is a REST API. But yeah, similarly the guides you’ll find will likely also work with general HTTP APIs.