Medicare helps millions of Americans, but it's a complex program that's hard for many to understand. Knowing the basics of Medicare is vital to make sure you get the benefits you deserve. To help you get the knowledge you need, you'll find short, simple answers below to some of the most common questions people have about Medicare.

1. Can I join Medicare?

U.S. citizens are eligible for Medicare, as are those who've lived legally in the U.S. for the past five years. However, as you'll see below, age restrictions apply to most people, and you could pay different amounts for your coverage depending on your income, work history, and marital status.

2. When can I get Medicare benefits?

Most people become eligible for Medicare when they turn 65. However, some people with disabilities or specific medical conditions like Lou Gehrig's disease or end-stage renal disease can get Medicare benefits before reaching age 65.

3. What benefits are available under Medicare?

Medicare has four main programs. Part A offers hospital insurance coverage. Part B handles medical costs like doctor visits and other outpatient expenses. Part D offers prescription drug plans. Finally, Medicare Advantage, sometimes referred to as Medicare Part C, is a private insurance alternative to Medicare, offering the same minimum benefits as traditional Medicare but also including supplemental coverage in some instances.

Medicare clipboard with stethoscope.

Image source: Getty Images.

4. How much does Part A hospital coverage cost?

Medicare Part A is free if you or your spouse has worked 10 years or longer in a job that paid into the program through payroll taxes. Hospital coverage is available at a cost for those with shorter work histories. The premium for 2017 is $227 per month for those with 30 to 39 quarters of qualifying work coverage, or $413 per month for those with fewer than 30 quarters.

5. What does Part A cover?

In general, Part A covers a portion of the cost of care in hospitals, skilled nursing facilities, hospice facilities, and in some cases, nursing homes. Home health services are also eligible for coverage. Limits apply to lengths of stay, with copayments generally increasing the longer you stay at a facility. The key is that care must be medically necessary, rather than simply custodial in nature.

6. How much does Part B medical coverage cost?

Medicare Part B almost always comes with monthly premiums. The standard premium in 2017 is $134 per month, but those with higher incomes pay surcharges that can take the total cost to as much as $428.60 per month.

7. What does Part B cover?

Part B covers a portion of the cost of medically necessary or preventive outpatient services and supplies. A wide variety of services are included, ranging from regular doctor visits and annual physicals to ambulance transportation, mobility equipment, and inoculations. You're typically responsible for a small percentage of the total cost of Part B services, with Medicare paying the majority.

8. How much does Part D prescription drug coverage cost?

Prescription drug plans under Part D vary in cost according to the specific coverage options they offer. Depending on the deductible, copayment amounts, and number of drugs covered, monthly premiums range from a low of $15 to $20 to as much as $100 or more. Higher-income individuals pay a surcharge of up to $76.20 per month on top of their regular premium.

9. What does Part D cover?

Drug plans make individual choices with respect to which drugs they'll cover. It's extremely important to check with a plan provider to make sure it covers the drugs you need. Otherwise, you might pay premiums for a plan that doesn't do you any good if it omits your prescriptions from its coverage.

10. When can I make changes to my Medicare coverage?

You can only make changes to Medicare coverage during eligible periods. The annual open enrollment period starts on Oct. 15 and ends on Dec. 7, and you can switch between traditional Medicare, Medicare Advantage, and various Part D prescription drug coverage options during that period. A special period also applies that allows you only to move from Medicare Advantage to traditional Medicare between Jan. 1 and Feb. 14.

11. Does Medicare take care of all of my healthcare needs?

No. Although Medicare covers many services, it doesn't pay the entire cost of all of them. If you have a catastrophic illness, then you could be left with huge medical bills even after Medicare pays its share. Medicare supplemental policies can protect you from what Medicare doesn't cover, and most Medicare Advantage plans also have out-of-pocket maximums and other protective features.

Medicare is vital for older Americans, and you need to know what the program will do for you in order to take maximum advantage of it. These questions aren't the only ones you'll have about Medicare, but they'll get you moving in the right direction toward getting the coverage you need.