Check out this link:
Employer Nomination Scheme (Subclass 121/856)
In order to fully understand your rights and responsibilities, I would recommend that you go through this section of the DIAC website very comprehensively. Best of luck!!!
By the way, could you shed some light on how you were able to obtain the ENS sponsorship? It remains a mystery to many how people are able to obtain 457/ENS sponsorship when Australian employers regularly prefer Australian educated/Australian resident workers. Indeed, I haven't seen many adds offering sponsorship!!!