Medicare enrollment begins automatically at 65 for those receiving Social Security, even if covered by a spouse’s insurance, while others must enroll manually. Part A is usually premium-free and commonly added at 65, but Part B has premiums and may not be needed if other coverage exists. Delaying Medigap or Part D enrollment can lead to higher costs and penalties. Medicare Advantage (Part C) offers combined benefits but may have higher out-of-pocket risks. Professional Medicare advice is often free through licensed agents.