Beneficiaries still enroll through Social Security to enroll into Medicare Part A & B benefits. You will still have to pay the Part B premium(Social Security deducted or Bank account). After you are enrolled into Medicare Part A & Part B you have a decision to make. Stay with Original Medicare(A&B) or enroll into the optional alternative, Medicare Advantage(Also known as Part C).
If you decide to enroll into the alternative, from here everything coordinates through your private insurance company. You will no longer receive a Medicare Summary Notice or have the ability to receive your eMSN through Medicare.gov. You will receive an Evidence of Coverage(EOC) and Explanation of Benefits(EOB) from your private insurance company that manages your healthcare cost typically through network of doctors and hospitals. Most common Medicare Advantage Plan types are Health Maintenance Organization(HMO) or Preferred Provider Organization(PPO). Note*. Check if your doctors are in network throughout the year. Also, prior-authorization and gate-keepers are common for both HMO and PPO's Medicare Advantage(Part C) Plans.
Below is a comparison chart between Medicare Supplement(Medigap) and Medicare Advantage(Part C). Medicare Supplements are also offered by private insurance companies. They cover the COST of co-pays, 20% co-insurance gaps and deductibles depending on the benefits covered by the Letter plan you enrolled into with the insurer. Fortunately, Medicare Supplement Letter Plans are standardized and federally regulated by the Centers for Medicare and Medicaid(CMS.gov). Compare Medicare Supplement Plans here.