I agree with Richard's answer. There are so many specialities, and then you can choose a specialty like cardiology, and get even more specific (pediatric cardiology). There are so many options in medicine but I will list a few of the typical ones. The best way to see what you like is to rotate with different specialities and get involved.
Cardiology: the heart
Neurology: the brain
Dermatology: the skin
Nephrology: the kidney
pediatrician: doctor that works with kids
OB/GYN: gynecologist is a doctor for females, an obstetrician is specifically for pregnant women.
Emergency Medicine: works in the ER
endocrinology: works with the hormones in your body
anesthesiology: helps puts patients to sleep during surgery and monitor them
Radiology: review and diagnose x-rays, CT scans and all other imaging
Pathology: a doctor that receives specimens (biopsies, blood, stool, urine) and helps diagnose the patient
orthopedic surgeon: doctor for bones, muscle and joint problems
ENT: ear, nose throat