In addition to all the advice about taking the time to review the offer, and then signing your acceptance, ask the new company for the earliest or most convenient start date.
I worked for one company that had a policy that they only started new employees on the first day of the pay period. They had the policy because they were hiring dozens of employees and had a whole day set aside for paperwork, required briefings, and mandatory training.
If you new company has a similar policy and you give your two weeks notice the day after you sign the offer, you could end up being unemployed for almost two weeks while waiting for the scheduled start day.
There is almost never a need to rush the process. They know that many employees have to put in notice with their old company, and the new company needs time to prepare for a new employee.