A doctor is a person who has studied medicine which is the science of taking care of people who are sick or injured. Doctors go to medical school for many years to learn how to diagnose and treat illnesses. When you are sick or injured, you can go to the doctor to find out what is wrong with you and get treatment to feel better. The doctor might talk to you, do tests, or prescribe medicine. Doctors can also help you stay healthy by giving advice on how to take care of yourself.