Medicare is a federal health insurance program primarily for people who are 65 or older. It also covers certain younger people with disabilities and people with End-Stage Renal Disease (ESRD) or Amyotrophic Lateral Sclerosis (ALS).

Part A: Hospital insurance that helps cover inpatient care in hospitals, skilled nursing facility care, hospice care, and some home health care.

Part B: Medical insurance that helps cover medically necessary services like doctor's visits, outpatient care, preventive services, and some medical supplies.

Part C: Also known as Medicare Advantage, this is an alternative to Original Medicare (Parts A and B) and typically includes Part D prescription drug coverage as well as additional benefits like vision, dental, and hearing.

Part D: Prescription drug coverage that helps pay for prescription drugs you may need.

You can typically enroll in Medicare during your Initial Enrollment Period (IEP), which begins three months before the month you turn 65 and ends three months after the month you turn 65. There are also Special Enrollment Periods (SEPs) for certain circumstances, such as if you continue to work past age 65 and have employer coverage.

While most people do not pay a premium for Part A if they or their spouse paid Medicare taxes while working, there are premiums for Part B, Part C (if you choose a Medicare Advantage plan), and Part D. The amount you pay can vary based on factors like income and the specific plan you choose.

The Medicare Part D coverage gap, often called the "donut hole," is a temporary limit on what your drug plan will cover for prescription drugs. Once you and your plan have spent a certain amount on covered drugs, you enter the coverage gap. During this phase, you'll pay a higher percentage of the cost of your drugs until you reach catastrophic coverage.