The K visa is an immigrant visa. When any US citizen is marrying any foreigner, the K-visa is very helpful to the foreigners who want to stay in the United States. This K visa divided into four types, which depends on the group. They won't consider whether the foreigner is male or female, but they will consider the age for considering whether the petitioner is children or younger or aged foreigners. The K visa applicant must answer the questions during the interview process and show all evidences about the marriage related documents at the local US consulate. The all K visa applicants must complete the DS-157 and DS-260 application forms.
The K-1 visa is suitable for fiance (e). The US citizens interested to marry a foreigner in the United States, and then the foreigner will be eligible to get a K-1 visa. Here the US citizen acts as a sponsor for obtaining a visa for foreigners. If the marriage canceled in any situation within the period, it's not valid. The US citizen and foreigner must show their proper evidences at the local US consulates.
The K-2 visa is a fiancee dependent visa. If the foreigner is already married another person, and has children, the children will be eligible for obtaining this dependent visa. But the age of the children must less than 21 years. This K-2 visa is applicable for children or wife or husband. The foreigner is already married and interested to marry another US citizen. In this case the foreigner's spouse will be also eligible to get this K-2 visa. But the dependents will have many restrictions; they must not do any other part-time or full-time jobs.
The K-3 visa is a spouse visa, the slight difference between spouse visa and fiance visa. The US citizen married to a person who is outside of the USA. Then the foreigner can come and settle in the USA, the US citizen applies a petition at the local US consulate. The foreigner also applies a K-3 visa at the local US embassy.
The US Embassy analyzes the petition and grants a visa for foreigners. The K-3 visa processing time is only three months, but if the applicant doesn't give the proper evidence, it's may take over six months.
The K-4 visa is a dependent visa like K-2 visa only, but this is for only fiance's children, but not the step children. The K-3 visa holder's children are also foreigners, so they are applying a visa with the help of K-3 visa holders.
The foreigner must have legally married according to the foreign country's rules and regulations. Then only US government agrees it as a legal marriage and grants a K-4 visa to the K-3 Visa and their dependents.
It is possible to get a green card with the help of K visas, so most of the people interested to apply these K visas and applications for K visa have increased year by year. It's too hard to get a K visa without an Immigration lawyer. It's highly recommended to take Immigration Attorney's help instead of applying K VISA by self.