Assuming you fulfilled the requirement of getting married to your U.S. citizen fiance within 90 days of having entered the U.S. on a K-1 visa, you are correct that it will be up to you to take the next step and apply for U.S. lawful residence.

We're assuming, of course, that a green card is actually what you want. Some people use a fiance visa just to get married in the U.S., and then leave afterwards.

The technical term for applying for lawful U.S. residence from within the U.S. is "adjustment of status." In brief, that means submitting various forms and documents to U.S. Citizenship and Immigration Services (USCIS), having fingerprints taken, and attending an interview at a USCIS Field Office.

This article will go over the basic procedures for the adjustment of status application.

Be aware, however, that the "green card" you receive will likely not be a permanent one. As someone who entered on a fiance visa, and only just got married, you're unlikely to have reached your two-year wedding anniversary by the time USCIS approves you for U.S. residence. By law, you will thus receive what's called "conditional residence," which will expire in two years unless you file an I-751 application to renew it.

Checklist of Forms, Documents, Fees

Here are the USCIS forms (downloadable from USCIS's website) and documents that you'll need to fill out or otherwise prepare (which in most cases means making copies of them and supplying word-for-word translations if they're not in English):

• Form I-485, Application to Register Permanent Residence or Adjust Status. The immigrant fills out and signs this. It's the main application used in requesting U.S. residence.
• Birth certificate. This helps prove your nationality and identity, and some family relationships. If your country issues both full and summary versions of birth certificates, provide the longer version.
• U.S. entry documents. These should include a copy of the biographical page of your passport, plus the page with your entry stamps; and your I-94 Arrival/Departure Record. If you didn't receive a paper I-94 from U.S. Customs and Border Protection (CBP) when you arrived in the U.S., download it from the CBP website.
• USCIS approval notice for the I-129F petition. This comes on a form marked "I-797."
• Marriage certificate. This must be issued by a government office.
• Four color photographs of immigrant. Two of these are for the employment authorization application discussed below. The photos must meet U.S. passport-style requirements; it's best to go to a professional photographer to have them done.
• Form I-864, Affidavit of Support. This must be prepared and signed by the U.S. petitioner-sponsor. Some sponsors can, alternatively, use a simpler version, the I-864EZ. The form must be accompanied by copies of financial documents proving that the U.S. spouse has the financial ability to support the immigrant. The affidavit also affirms that the U.S. spouse is in fact willing to provide financial support to the immigrant, thus making sure that he or she won't need government assistance for approximately the next ten years. This is a binding contract, and continues regardless of whether the couple gets divorced. Also see Is My Family's Income Too Low to Get Me a U.S. Green Card?
• Form I-765, Application for Employment Authorization. Even an immigrant who doesn't plan to work in the U.S. can benefit from receiving a U.S. photo ID authorizing working in the United States. It's useful for identification purposes. And it costs nothing extra when submitted with an I-485. It will last until USCIS approves U.S. residence, at which time the green card will serve in place of a work authorization card.
• Form I-131, Application for Travel Document. If there’s any possibility you might travel outside the U.S. before USCIS approves you for residence, definitely submit this application. (It costs nothing extra when submitted with an I-485.) Without receiving “Advance Parole” by use of this form, your departure from the U.S. will cause USCIS to view your application as "abandoned," and cancel it.
• Form I-693, Report of Medical Examination and Vaccination Record. You already had a medical exam as part of getting your K-1 visa. But if it's going to be over a year old by the time you apply to adjust, or if the physician reported that you have a Class A medical condition for which you didn’t get a waiver, you will need to get a new exam from a USCIS-authorized civil surgeon. And even if your earlier exam is still valid, you might have to see a civil surgeon if the physician in your country didn’t include a complete vaccination record (DS-3025).
• Fee for adjustment of status. For most adults, this comes to $1,225 (in 2019), but see USCiS's I-485 page for details and updates.
• G-1450, Authorization for Credit Card Transactions. Include this if you'd like to pay USCIS the application fee by credit card.

After compiling all of this, make a complete copy for your own records and send it with your check, money order, or credit card form to the address indicated on the I-485 page of the USCIS website.

If this seems like too much paperwork to deal with on your own, of if complications are present in your case (such as a recent arrest or loss of household income), consult an attorney.

USCIS Appointment Scheduling

After you've mailed everything in, USCIS will send you a receipt notice, containing instructions for how to check its progress through the agency's processing. Be warned, long waits are common.

At some point, you'll receive notice to attend a biometrics (fingerprinting) appointment. Later, you'll receive an interview appointment notice. Both the immigrant and the U.S. citizen must attend this. It will be held at a USCIS office in your state.

If you change addresses, be sure to let USCIS know.

Attending Your Adjustment of Status Interview

Prepare to bring with you a photo identity document, originals of all the copies you submitted, and any official documents showing changes to the material in your application (such as a legal name change). Also bring documents showing the your marriage is bona fide (real), not a fraud to get the immigrant a green card.

Arrive well ahead of your appointment time, because you'll need to get through a security checkpoint (it's a federal building). Also, if you're late, you might have to return on another day.

The interview itself normally takes around 20 minutes. A USCIS officer will swear you in, ask questions to make sure the information on the application is correct and that the immigrant isn't inadmissible, check the results of the immigrant's fingerprint report (which is run through FBI and other databases), check the medical exam report, and ask questions about your marriage.

Proving a bona fide (real) marriage is one of the most important parts of the interview. The officer will ask questions like, "How did you meet?" "How many people attended your wedding?" and "Does either of you set an alarm clock in the morning, and for what time?" If one or two of your answers don't match perfectly, that may be understandable.

But if it appears that the two of you don't really know enough about each other to possibly be sharing a life, you might be taken to separate rooms for a longer interview. An officer will ask each of you identical questions and then compare the answers. This could result in a denial of the green card.

If all goes well, your residence should be approved on the interview day or soon after. Your green card will come by mail some weeks later.