I have been told that if I don't sign up months before I turn 65 I am not eligible.
What does it cover or not cover?
What supplemental plans are good, bad, necessary, or not needed?
K Cummings's Link
It's not complicated, but it can be confusing.
First, Medicare part A (hospital coverage) is automatic. Part B (physician coverage) is voluntary and requires the enrollee to sign up within a certain enrollment period.
Part D (prescription drugs) is also voluntary.
The coverage you need depends on what your employer coverage does, what prescriptions you take, and what kind of deductibles and copays you want.
I would recommend you start with your local SS office (or reading the publication at the link) and they will explain the enrollment periods and sign up . Then I would contact a competent insurance agent, one that knows the medicare supplement plan options (not usually your house and car guy) and have them advise you regarding all your options.