WiFi connection @ campground.

Connecting to the campground's Wi-Fi should be no different than connecting to any other Wi-Fi, whether its at home or a public location like a hotel, library, Starbucks, etc. The campground wireless administrator should be able to provide you with both the Wi-Fi's Network Name (or SSID) and password if it's a secured network. In turn, you would use the AirPort menu on your iMac to select this network from the drop-down list ... and, if required, enter the appropriate network password to connect.