When you arrive go to the office to check in, then they'll show you available campsites. Best to get there early (after 2pm).
You reserved a certain area in Garner park. You can't reserve a specific spot just a specific general area. You wait in line to check in and thats when you pick a good spot from the map.
Henry if you're going to camp overnight for several days and have several people in your party; consider the annual State Park pass as an option. You'll save a few dollars on this stay and gain free entry option at every state park for a full calender year. Get there as early as you can though and "take a number" because once they open they use the number system to call people in to pay.
It secures that there will be an available campsite, but they are chosen on a first come basis.
You will have to choose the campsite on check in.
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