All your answers will be revealed -------> help.sap.com 
You did not mention anything about what version you are looking for either....that will help narrow down your answer though ESS has changed very little over the years (most services are the same from years back.....only the underlying code implementations changed....ITS to Java WebDynpro to ABAP WebDynpro to UI5 )
....and please always Always ALWAYS search before asking a question. This has been asked before.
Here is a list of the newer UI5 services...