Kathie, you can go to the medicare website, "www.medicare.gov/" and get information relative to your zip code.
You can also check with your county, they will have a SHIP, which is State Health Insurance Assistance Program. They will have the same software you can get at the medicare gov site, but you will have a human there who does it frequently to help you. They will give you choices, cost, phone numbers, or can enroll you if you ask them to. You usually just call to set up an appointment.
You mentioned a Medicare Gap plan F, which indicates to me you may have a need for more then average coverage. Be aware, when you FIRST sign up for medicare you have a 6 month open enrollment, but the next year rolls around for open enrollment you if you did not sign up for the better coverage at the beginning they can charge you an increased premium over other in the group.