You become eligible for Medicare, which is a federal health program, when you turn 65 years old. You're also eligible if you've been collecting Social Security Disability Income for 24 months or diagnosed with End-Stage Renal Disease. There are two main parts to Original Medicare. This includes Part A and Part B. Part A is your hospital coverage and Part B is your doctor and medical coverage. 

When it comes to signing up for Medicare. Some are automatically enrolled in others will need to actively enroll. If you've been collecting Social Security benefits for at least 4 months, you'll be automatically enrolled into both Parts A and Part B. Your effective date will be the first day of the month you turn 65 years old. If your birthday happens to fall on the 1st of the month then your effective date will be the 1st of the month before your birthday. For example, if your birthday falls on July 1st, then your effective date will be June 1st. 

You'll receive your Medicare card around 3 months before your birthday. If you're not collecting Social Security benefits, then you'll need to actively enroll into Part A and Part B. You'll want to enroll during your Initial Enrollment Period. Your Initial Enrollment window will be 7 months and starts 3 months before your birthday, will last the month of your birthday and will end 3 months after your birthday.

There are three ways you can enroll in Medicare. The 1st way is going down to your local Social Security Office. The 2nd way is to go ahead and give the Social Security office a call to enroll. The 3rd way and probably the most easy way is to do it online.

To begin the online application process you'll need to visit Social Security's web site. That's ssa.gov/benefits/Medicare. Then you'll scroll to the bottom of the page until you see the big blue button that says apply for Medicare only. If you recently have started an application and did not complete it, you can return to your saved application here also. It will bring you to the next page that talks a little bit about the online application and an option to start a new application. So go ahead and select start a new application. And then it will ask you if you're applying for yourself or someone who's not with you. So select applying for myself. Then it will ask if you have a My Social Security account. If you do not have one you will need to create one. If you do have one it will then ask you to sign in. So let's assume that I currently do not have a My Social Security account. You will need to have an address that's within the United States and US Territories to create the account. So select yes and hit next. At this point it will bring you to secure.ssa.gov to create an account. At this point it's going to ask you a few personal questions. The form will take about 15 to 20 minutes to fill out. If you would like you can save it and complete it later.

You will receive a letter from Social Security Administration once they made a decision about your enrollment. 

Now, if you only have Part A and you delayed enrolling into Medicare Part B there are two additional forms that you'll need to complete to enroll in Part B. 

So if you already have Part A and you're only enrolling in Part B, then you'll need to also complete 40B form. Which is application for enrollment in Part B. Once you complete this form, you'll want to include it in your online application or mail into the Social Security office. Now, if you delayed Part B due to having group employer coverage, you'll also need to complete the L564 form. Which is request for employment information.

MedicareFAQ: https://www.medicarefaq.com/faqs/applying-for-medicare/
Social Security Website: https://www.ssa.gov/benefits/medicare/
40B Form: https://www.cms.gov/Medicare/CMS-Forms/CMS-Forms/Downloads/CMS40B-E.pdf
L564 Form: https://www.cms.gov/medicare/CMS-Forms/CMS-Forms/Downloads/CMS-L564E.pdf