When you submit your reservation request, it is sent straight to the campground. Once the availability and pricing of the request have been confirmed, the reservation will be approved and the payment will take place at this time. If there is no availability or another reason for the request to be rejected, you will not be charged a fee.
With campgrounds that have an Instant Book option set up, your reservation will automatically be approved and you will be charged right away. You can tell the Instant Book sites by the lightning bolt next to the campground.