What site will you be camping on? You will need to know two things: the Loop and the Site Number. You can find this info in two ways.
1) Check the confirmation email you got from Reserve America when you booked the site.
OR
2) Log in to your Reserve America account, then go to "My Reservations" in the menu under your username at the top right of the screen.

For example, in the reservation above, the site is "BS-05," circled in red. This means Loop B South, Site #5. "Site A-11" would be Loop A, site 11; "Site BN-21" would be Loop B North, site 21, etc.