There are no required credentials to be a professional photographer. The most important requirement is talent, either natural or learned.
There are a large number of books and videos available to help you train yourself to be a photographer. One drawback to self teaching is a lack of constructive criticism on your work.
You can take lessons through local museums and art associations. It may also be possible to get one on one instruction from private photographers.
Colleges and some professional art associations offer complete programs that teach all aspects of photography. These are non-credit community programs that you can take.
While it is not required to get a degree to be a photographer, many people pursue a degree in art with an emphasis in photography. This looks more impressive on a resume.