Visit the Social Security Administration website at ssa.gov. 

Select "Sign up for Medicare" on the home page under the Apply heading. 

Follow the appropriate prompts on the sign-up page:

On the Social Security website, a person can enroll themselves into Medicare or sign up for Part B only. 

Typically, a person would only need to use the "sign up for Part B only" option if they delayed Part B enrollment because they already had creditable coverage and already have Part A. As a reminder, the beneficiary that did not take their Part B because of creditable coverage through their employer will have an 8-month enrollment period to enroll in Part B when they leave their employment and their creditable coverage ends. 

Call Social Security Administration at 1-800-772-1213, Monday - Friday, 8am to 7pm. 

Make an in-person appointment at a local Social Security office.