It has four main parts, labeled A, B, C and D. But after that, the rules can be wickedly complex. Nearly 60 million people are using it right now. And with an estimated 10,000 people reaching age 65 each day in the U.S., that number is growing fast. So, yes, Medicare is as big as it is complicated. And as the Medicare annual enrollment period begins today, the Tampa Bay Times aims to help readers better understand this massive but immensely beneficial public health care program, now in its 52nd year. The enrollment period, which ends Dec. 7, is an important time for both retirees just entering the program and those who have been enrolled for years. We explain how Medicare is set up, help you examine and compare the options available in your area, and point you to places where you can find out more. Click on the links below to access our 2019 Medicare Guide: • GETTING READY: A look at what you need to know as we enter the enrollment period — from Medicare basics to tips on how to use the program to your best advantage. • SHOPPING AROUND: Our chart allows you to compare dozens of Medicare Advantage plans with drug coverage available in Hillsborough, Pinellas, Pasco and Hernando counties. • PRESCRIPTIONS: Another chart compares standalone plans available in Florida under Medicare’s Part D program for prescription drugs. • STEP BY STEP: A great way to thoroughly compare your options is through the online Plan Finder at medicare.gov. We’ve been there and can walk you through it. • STARTING TO SHINE: A state program called Serving Health Insurance Needs of Elders, or SHINE, offers information on events around the area and has volunteers to take your questions — in person, online and over the phone. Find the details here.