Part A is your hospitalization coverage and the first part of Medicare you will receive. Part A has no premium because you funded it while working. As long as you have worked for 40 quarters (10 years) you will receive Part A on the 1st of the month you turn 65. For 2020 Part A has a $1,408 deductible when admitted to the hospital after that Medicare covers the majority of costs.
Part B is your medical (out-patient). Once you have chosen to elect Part B, there will be a monthly premium (average premium $144). Part B will cover 80% of your costs and you are responsible for the remaining 20% and a annual deductible of $198 (2020). Popular services covered under Part B are doctors visits, specialist, outpatient surgery, rehab, observation, lab work, MRI, and cat scans.
This is known as a Medicare Advantage Plan or MAPD. They are either an HMO, PPO, PFFS, or MA only. They are government ran and replace your Part A and B of Medicare. You are still responsible for roughly 20% of all medical costs plus co-pays. Most Advantage Plans are network based. You can purchase a Medicare Advantage plan with or without prescription coverage. Typically Medicare Advantage Plans can be purchased during the Annual Enrollment Period.
These are stand alone prescription plans.They are government run. Changes can only be made to these plans during the Annual Enrollment Period. They allow you to get your prescriptions at a discounted rate. If you do not enroll in a plan or have a credible drug coverage through some other means the government will penalize you when you do enroll.