Do you need an vaccine to travel ? Or just if you going out the country

Only if leaving or entering the country, is my understanding

Only if you are flying internationally

Only if leaving country. You don't need it to fly within the United States

It is required to have the Shot to avoid quarantine

It is all dependent on the country policy. Others will require it and still need to quarantine when you arrive. Highly suggest to do your research specific to the country.