What is the difference between Medicare Part A and Medicare Part B? 

Medicare Part A is hospital insurance.  It covers inpatient care.  This includes skilled nursing access, but this is not to be confused with long-term care.  Hospice and other home health care are part of Medicare Part A. 

Medicare Part B is medical insurance.  It covers services provided by the doctor, physical and occupational therapy, some home health care, and very importantly outpatient hospital care.  Some preventative services are also covered.  They include:  bone mass measurements, colorectal cancer screening, diabetes services, glaucoma testing, pap test and pelvic exam, prostate cancer screening, mammograms, the vaccination shots.

How do medicare supplements fit in with Medicare Part A and Part B?  Medicare Parts A and B have deductibles and coinsurance that the medicare recipiant is responsible for.  Medicare Supplement Insurance protects the insured from these risks.