What is an API and how does it work?

An API is a contract: the shape of the request, the shape of the response, the errors that can come back, and how you prove who you are. Everything else about the system behind it is deliberately hidden, which is the point — the provider can rewrite their internals entirely and your integration keeps working as long as the contract holds.

Every third-party integration is a dependency that will eventually be slow, rate-limited, or down, and your application has to have an answer for that other than hanging. Timeouts, a retry policy that backs off, and a sensible degraded state matter more than the happy path. It is also worth checking their rate limits against your expected volume before you build, not after the first busy day.