Hi,
I just bought a used rv that came with a sattelite dish on the roof. What else do I need or need to do to use it?

Assuming that it's for satellite TV and not Internet service, you need to obtain a receiver from the satellite TV provider of your choice. You should know that unless it is a fairly recent, expensive unit, it will probably not receive HD TV or all of the stations available from either Dish Network or DirecTV.

If you are new to this, I would take the RV to an RV service facility that sells either Dish Network or DirecTV service. They can look at your dish and tll you what your options are.