Extension of h4 visa details


I got my H-4 visa stamped on june-2015.And i went to pheonix and stayed their for 2 months. And i returned to india after 2 months and i am staying in india untill date. And my visa is going to expire on apirl-2017. I want to know the details of how to extend my visa (or) i should renew my visa. I dont know about any visa process. For extension/renew do i need any of my spouse documents(is it mandatory).And i want to know where i can renew/extend my visa process First time i got renewed at cheenai.And want to know what is h4(EAD).

Thank u