I can't figure out how to use Recreation.gov

The dates you enter on the calendar don't do much, as mentioned above you have to find the A's on their availablity calendar and find a site with the range of dates that you want and select it. Generally Friday and Saturday are very tough to reserve since the locals come out and lock up those weekend dates.
We are at Potter Creek COE in Texas righgt now and I had to settle for one night in one campsite and then move to another for Monday to Friday (departure)
We stayed at about 15 COE camps over the last year or so.