Regardless of what they decide to do with their time, one shared milestone for those turning 65 is their eligibility to enroll in Medicare.

"The transition from employer-sponsored health insurance to Medicare can be nearly seamless for those whose health insurance provider also offers Medicare plans," said Tom Paul, chief executive officer of UnitedHealthcare Medicare Solutions, which serves nearly 9 million--or one-in-five--Medicare beneficiaries nationwide.

For other new enrollees, however, enrolling in Medicare can be a challenge. To make enrollment as clear as possible, Paul encourages adults turning 65 to focus on three key things: the types of Medicare plans that are available; the enrollment process; and annual opportunities to make adjustments to coverage.

1. The ABCs-and D-of Medicare: Medicare has four main parts.

• Part A helps pay for inpatient care in hospitals, skilled nursing facilities or hospice and for home health care if certain conditions are met.

• Part B helps pay for medically necessary outpatient services, such as doctors’ visits.

• Part C is also known as Medicare Advantage. These private plans are offered by insurers such as UnitedHealthcare and are approved by Medicare to provide all Part A and Part B services, and they usually provide Part D and other additional benefits.

• Part D covers both brand-name and generic prescription drugs.

Medicare Supplement, or Medigap, plans are also available to help fill in some of the gaps of Part A and Part B coverage.

2. Enrolling in Medicare: Adults who are turning 65 and have not yet begun receiving Social Security or Railroad Retirement benefits can apply for Medicare three months before the month of their 65th birthday, during the month of their birthday, or within three months following their birthday. Eligible individuals can enroll in Part A at no cost. They can add Part B coverage for a monthly premium paid to the federal government. Part D is also a voluntary election with an additional monthly premium. Those enrolled in both Part A and Part B can choose to receive this coverage through an "all-in-one" Part C--better known as Medicare Advantage--plan, which combines Parts A and B and also often includes Part D.

3. What to Expect in Future Years: Each year, Medicare enrollees can make changes to their Medicare coverage during the Annual Election Period (AEP) from Nov. 15 to Dec. 31. The new health reform law changes the dates of the AEP beginning in 2011, when it will last from Oct. 15 to Dec. 7.