I'm getting ready to book a reservation but I don't know what address I will be dropping him off at?

Christy,

It is really a good practice to request a Meet & Greet with potential sitters and then make a decision which one best fits your needs. When you set up a Meet & Greet, you message with the sitter and they will give you their address.

If you go ahead and book blindly, and the sitter accepts the booking blindly, then Rover's confirmation will have the pertinent information about the booking, including the address. But nothing prevents you from asking sitters directly for that information via messaging within the app.