There are many different kinds of visas required to enter the United States, varying depending on purpose, use and country of origin. However there are some things that are required across the board regardless of what you apply for. Here are some examples of the more popular visas that people tend to apply for. Please note that regulations may change and that for specific info you should consult with an immigration lawyer or your local consulate.
The border crossing card visa designated as B1 or B2 is a visa designed for crossing into the United States. The B-1 visa is specifically designated for those who are visiting the United States for business reasons. The B-2 visa is designated for those who are visiting for pleasure purposes such as tourism, visiting family or social events such as a concert. There are several steps involved in applying for one, first is to schedule an interview with a Embassy or Consulate, with the exception of those who are 13 and lower, or 80 and older. Next is to gather the required documents needed for the interview. It is vital that you ensure you have all the documents needed before you arrive at the interview otherwise it is likely you will have to reschedule the meeting for another time. If approved you may enter the United States beginning on the date of the visa, however it does not guarantee entry and you may still be denied by Customs officials. You must depart on or before the date indicated on your admission stamp unless you receive permission from US Citizenship and Immigration Services. Failure to do so may result in you becoming ineligible to receive visas in the future.
Another type of visa that is offered is known as a transit. This is designed for those who are traveling through the United States on their way to another country. Transit is defined as a timely departure during a normal course of travel. If one is going to be remaining in the United States for a purpose other than transit, then a different type of visa is required. There are just a few steps to apply, first thing to do is complete the visa application online. During this application you will be asked to attach your photo, the photo must be properly formatted according to the photograph requirements. Upon completion of this step, you will receive a conformation page which you will need to bring to your interview. The next step is to actually schedule the interview, wait times may vary depending on location so be sure to check your local office. As with most visas there is a nonrefundable fee that you may need to pay before the interview. Be sure and gather any required documentation you may need such as passport, application fee receipt, etc. Once the interview is complete if approved you will learn how you will receive your passport with visa either via pick up or delivery.
If you are a worker from Canada or Mexico you can apply for the North American Free Trade Agreement (NAFTA) visa, also known as TN. Like the C visa mentioned above the first step is to complete the online application with a photo of you attached. Once this is complete you will need to schedule an interview and potentially pay the application fee if it is required before the interview. For the interview aside from your passport and confirmation page you will also need a contract or letter of employment. This must include the following, your purpose of entry, description of job responsibilities, anticipated length of stay, job qualifications, and evident that you are complying with Department of Homeland Security regulations. Next you will need to provide documentation proving that you meet the minimum education or work experience requirements as required from NAFTA chapter 16. Once the interview is complete upon approval the officer will explain how you will receive your visa. If you wish to have your spouse or children join you later, you will need to show your ability to financially support them in the United States before they can apply for a TD visa.).
However say you are engaged to someone who is not a US citizen and wish to get married in the United States, in that case you would need to file for a nonimmigrant visa for fiancé also known as a K-1. This visa permits you to marry your foreign bon fiancé within 90 days of arrival. Once married your fiancé will then need to apply for status as a permanent resident. According to US immigration law the couple must have met in person within two years and the marriage must be legal in the state where the wedding is taken place. The first step is to file a petition through Form I-129F. If this petition is approved it is then sent to the National Visa Center (NVC) who will give you a case number and send your petition to the embassy or consulate where your fiancé resides. When this occurs the NVC will send you a letter in the mail at which point you should inform your fiancé to make sure they have the documents required such as a passport, evidence of financial support, photos of you together, etc. The two of you will then interview with a consular officer and if everything is in order the visa will be issued. If your fiancé has children there may or may not be additional requirements depending on age so it is highly recommend to check with your local embassy or consulate for details.
From beginning to end the road receiving a visa to enter the United States can have many turns. From determining the purpose, gathering the correct documentation, interviewing and getting approved it can take months. However by planning ahead of time and coordinating with the appropriate officers your chances of success will likely be much higher.