There's a full open API schema served by the API server. Tools can read it and build specific interfaces or validate requests before even sending them. And in general k8s is really just a big database of objects. Once you learn the core objects like pod, deployment, service, etc. it becomes very natural to interact with anything else--just find what object it is and interact with its attributes.
I guess this means that you're able to learn how the API works by using the API to download metadata.
In fact, one can generate a complete API client by pointing a script to a running kubernetes instance, which will generate all code for interacting with exactly that version. And the resulting client is huuuge.
