Welcome to the forum, Samantha.
In answer to your question(s).
1. Once you arrive at your destination, remove the car from the dolly. Move the dolly to the prescribed location. Often this is somewhere within the campsite. Many times they're slipped under the rear of the coach. Other times the campground has a dedicated spot for trailers/dollies/extra vehicles.
2. Many campgrounds ask you to unhook your towed vehicle due to the narrow/curvy roadways. In this case it is advantageous to have a tow hitch on the towed vehicle so you can use that to move the dolly. If it's required that you unhook your dolly, they will have a place for you to do so.
3. If your towed vehicle does not have a hitch, many campgrounds have a golf cart with a ball attached that can move the dolly to your site or wherever they require it to be.
4. Other campgrounds have no limitations so you pull in, register, drive to your site, dismount the towed at your site and muscle the dolly under your coach.
Now my recommendation. Unless you absolutely have to use a dolly, towing four down is more convenient, easier to hook up and unhook and eliminates everything you've asked about....best of luck and happy camping....Dennis