The application process is generally not very lengthy and the eligibility process is not as complex as other family based Visas. If you petition for a fiancé(e) visa you must show that:
1. you are a US citizen,
2. you intend to marry your fiancé(e) within 90 days of entering the United States,
3. both parties are free to marry and not encumbered by any previous marriages, and 4.) you have met each other in person at least once within the last 2 years. Except, strict religious customs, cultural or social practices prohibit meeting or meeting in person would result in extreme hardship to you.
Once all hurdles are cleared, the finance(e) is issued a K-1 nonimmigrant Visa to enter the United States for 90 days. The marriage must take place within those 90 days. After you are married, your spouse may apply for permanent residence and remain in the United States while the application is being processed.
Your spouse can apply for an authorization to work in the United States. If your spouse has a child (or children) under the age of 21 and unmarried, a K-2 nonimmigrant Visa maybe available to them. Just make sure to include the names of the children on the petition for your fiancé(e).
The fiancé(e) Visa status will only be valid for 90 days and will automatically expire.
No extension will be granted, and your fiancé(e) will not be allowed to switch to another Visa category. Your fiancé(e) must leave the US if the marriage does not take place within 90 days of entering the United States. Failure to leave may result in removal (deportation) and/or could affect future eligibility immigration benefits.