Indeed, the sparsity of "how to use it" is one of the reasons many developers were left out when steemit quickly jumped over.
Basically, it has taken many of the API calls, such as those from here:
https://developers.steem.io/apidefinitions/#apidefinitions-follow-api
And replaced the way they are responded to with a different program, in an attempt to save costs.
The GitHub shows which calls were replaced.

Otherwise, it should be the same semantics for using an API node -- it's the back end that a front end like an app talks to.