When you arrive at the entrance to Tsodilo you will discover a small museum explaing all about local beliefs surrounding the area and geological information about the hills, hanging around this place you will find local San (bushmen) who will offer to guide you on walks on and around the hills, if you want to see the san art you will need thier help... negotiate a price and times for walks.
There is no official charge for staying overnight at Tsodilo they just request a donation towards the upkeep of the museum and keeping the area clean, donations should be made to the museum donation box only, NOT to any 'official' wandering around! The free camping sites are really areas of cleared bush dotted among the hills, no facilities of any kind, no ablutions (dig your own), no water (bring your own), no lights (light your own), absolutely nothing, there is also no shop for 80km (in Shakawe).
After you sign in at the museum you can proceed through the gate and into the hills. There is no allocation of sites so its drive around looking for a spot that looks nice. The road is very sandy, the areas among the trees more so.