Someone else has 1st dibs on it already. But to answer ya question, it has an elasticated skirt that fits over the roof of the vehicle it's attached to. When you want to drive away there's a door that zips close.
The tent part stays where you put it up, the vehicle is free to come and go as you like, just the same as any other tent. The beauty of it is the elasticated skirt seals to the vehicle again so, for instance, you can still use the boot area as a camp store, cooking, whatever .. Un-seal it to drive to the shops, seal it again when you return, or leave the tent free standing and just sleep in it without sealing it to the vehicle!