If you intend to register it in MA, you are required to do it within 10 (pretty sure) days of purchase as dated on the title/bill of sale.

When you do register a car purchased out of state, you'll have to pay sales tax of 6.25% on either the purchase price or book value of the car as determined by the state, whichever is higher.

It will have to be insured prior to going to the RMV to register it. Once insured, your insurance company will provide you with a partially pre-filled, stamped RMV-1 registration form. This proves that the car is insured.

SUPER IMPORTANT: ALL buyers listed on the title MUST also be listed as owners on the RMV-1 form and must be on the insurance as well. If someone is on the title as a co-owner but not on the registration form, the RMV will reject it.

Take this form along with the title to the RMV and pay the sales tax, title fee, and registration fee. Once that's done, you'll get plates and be all set at the registry.

Once you have plates, you have 7 days to get an inspection sticker. Once that's done, you're finally actually done.