In some cases, it isn’t necessary to sign up for Medicare because some people get Medicare Part A and Part B automatically. If you are already collecting Social Security benefits, you will be automatically enrolled into Part A and Part B.
If you aren’t collecting Social Security, you won’t be automatically enrolled into Medicare. You’ll need to sign up through the Social Security Administration. This can be done in-person at a local office, over the phone, or online here: https://secure.ssa.gov/iClaim/rib