Millions of older Americans are enrolled in Medicare. But being enrolled in the program does not automatically equate to understanding all of its inner workings and rules.

Such is the result of a recent MedicareAdvantage.com survey, which found that almost 65% of enrollees say the program is confusing and difficult to understand. If that's how you feel, here are a few big myths you should know not to buy into.

A person wearing scrubs talking to a seated person.

Image source: Getty Images.

Myth No. 1: Medicare coverage is free

Medicare is often hailed as an affordable means of securing health insurance for seniors. But that coverage comes at a cost.

The only part of Medicare that's free is Part A, which covers hospital care and skilled nursing facilities (and it's worth noting that while part A is free for most enrollees, it may not be free for everyone). Part B, which covers outpatient care and diagnostics, charges a monthly premium that enrollees either submit directly or have deducted from their Social Security benefits.

Then there's Part D, which covers prescriptions. Part D plans set different premium rates, and the cost from one plan to the next can vary. But there's a cost nonetheless.

In the aforementioned survey, almost 24% of enrollees thought that original Medicare covers prescriptions. But you'll need a Part D plan if you want your medications covered to some degree (meaning you might still have a copay, but that's better than having to cover 100% of your medication costs).

Myth No. 2: Medicare allows you to see any doctor

Enrollees in original Medicare -- Parts A and B, plus a Part D drug plan -- typically get access to a wide range of healthcare providers. But that doesn't mean you can see any doctor you want. Unless you're willing to pay out of pocket, you'll need to make sure your doctor accepts Medicare.

Also, if you're enrolled in a Medicare Advantage plan instead of original Medicare, you'll generally be limited to a specific network of providers. Going out of network could result in huge out-of-pocket costs.

Myth No. 3: You have to commit to original Medicare versus Medicare Advantage forever

Enrollees in Medicare are given the option to choose between original Medicare and Medicare Advantage. But you're not stuck with your decision forever.

Each year, between Oct. 15 and Dec. 7, Medicare enrollees get the opportunity to make changes to their coverage during annual open enrollment. In the course of open enrollment, you can move from original Medicare to Medicare Advantage or drop Advantage and get on original Medicare. Make sure you know how your benefits will change with any switch. You might be losing coverage. You can also switch from one Advantage plan to another that better meets your needs or is more cost-effective. 

In the aforementioned survey, 26% of respondents did not know when open enrollment begins for Medicare participants. So if you're a current beneficiary, now's the time to explore changes to your coverage.

Clearly, there's a lot of confusion out there about Medicare. If you're an enrollee or are about to sign up and you feel that you're in the dark, take the time to read up on the program's costs and rules. The more you learn about Medicare, the better equipped you'll be to set yourself up with the right health coverage and avoid financial stress in the course of paying for your health-related needs.