What is the purpose of full faith and credit clause?

The Full Faith and Credit is a provision of Article IV, section 1, of the Constitution. It requires states to honor the civil rulings of other states. It simply means that civil acts like driving licenses, marriage certificates, judicial actions, and other records and public acts are recognized in all states. That does not mean that all certified professions are recognized in all states automatically. A lawyer or doctor may have to apply to get a license to operate if he/she moves to another state. Teaching certificates also have to be approved by each state. Some states cooperate on recognizing such certificates.