All endpoints are registered at /mailcoach/api (or /api in the stand-alone installation) using the default configuration, you can change this when registering the route macro. From there on, you will find a logical structure that follows to the REST standard.
Here's a quick summary of the API methods.
GET: all GET requests are for data retrieval only and will never modify any data.
POST: a POST method will add new items to Mailcoach
DELETE: the DELETE method is used to delete items.
PUT: this method is used to update information on existing items.
In general, GET requests can be performed as many times as you'd like (they are idempotent), all other methods actually transform data in your account and will cause changes to take effect.