I took some classes and passed the final exam and got a certificate. I really want to start babysitting.

Then with the help of your parents find some family that will let you baby sit ?

Like Fr_Chuck said, talk with your parents about anyone they know who might need a sitter, or maybe, since you are just starting and getting a reputation as reliable, find a family or two that needs a mother's helper -- a sitter who spends time with and plays with the children while the mom and dad do chores around the house. That can then move into your being alone with the children while the parents leave the house without dragging their kids along to grocery shop or go out to eat or visit someone in the hospital.