Selling car registered, questions about safety

Hello everybody, I hired my car earlier at mobile.de. Someone who wants to come by tonight with money to buy the car. But now the car is still registered. How is it with the insurance? Can I give him the car registered with? And, I saw that on my vehicle ticket in the back there is such a scratch field with which you can log off the car. how does it work, can I get home tomorrow morning when he is with the wagon, that Then register the car online and I am out of liability for the vehicle? And, suppose he has a nfall on the ride today, where is that going with the liability then?. What should (in such a case you have to write in the purchase transcript? Sorry for the many questions, but that comes now all a bit sudden.. MfG prikkelpitt