To see all of the endpoints available, log into your AdminCP and go to System -> REST API -> API Reference. It will automatically show you the endpoints for the applications you have available and for the version you are running.
Each endpoint will have several sections:
Shows all of the parameters you can send in your request. For GET requests, send these in the query string, for POST and PUT requests, send as the body of your request URL Form-Encoded.
Unless specified, all parameters are optional.
Describes the errors that may be returned if the parameters you provide are not valid. For more information about errors see Understanding Errors.
The response is usually a JSON-encoded object with the elements described. If an endpoint has no response, it will be a JSON-encoded null.
If the response contains other objects, the structure of each of those objects is then described.