If you ask what is Medicare Part B? Then the answer would be, that it is the part of Medicare that provides medical insurance. You can use it to cover various outpatient services. It is included within Original Medicare. The importance of Medicare part B covers a wide variety of medically necessary outpatient services. It covers two types of services such as: Medically necessary services: Services or supplies that are needed to diagnose or treat your medical condition and that meet accepted standards of medical practice. Preventive services: Health care to prevent illness (like the flu) or detect it at an early stage, when treatment is most likely to work best.