Bought used car in Massachusetts can i drive it?
you heard wrong.
You need to insure the car to register it, and you need to register it to drive it. There is no trial period - if you get caught driving an unregistered and uninsured car, the police can arrest you, and if you get into an accident, you can get sued.
EDIT - you need to inform your insurance company of the change before the new car is covered, but you still need to register it. That's the law - if you have any doubts, ask a cop, he/she will confirm what I'm saying.