You start with Medicare A and B. The pricing depends on your income level, but I think the range is like $130 to $200 a month. Next is your supplemental, which can be Medicare Advantage or Medicare G. Advantage is like an HMO and can be free to very low cost, but like an HMO you need approval for care. G is like a PPO and runs about $130-$150 a month . Unless you have a favorite provider, it doesn't matter who you pick, because all the terms are identical and the prices vary only about $20 a month, and apparently tend to be the same over time. As long as your doctors accept Medicare G , there is a small deductible, I think about $250 a year, and 100% coverage after that. My wife's knee replacement was free, for example.
Lastly you need a Prescription plan. These all vary based on the drugs you take. They can be free or as much as $100 a month.
Once you pick Advantage or G for your supplemental it tends to be a permanent decision, because if you want to change between the 2 or change providers, you have to medically qualify to change. You can change drug plans every year without a problem.
If you don't make these decisions within the enrollment period, there can be both time and financial penalties, and they may be permanent penalities.
I've got a good Medicare insurance agent, if you're interested.