K-1: the fiance visa
The K-1 lets a US citizen bring a fiance to the United States to marry within 90 days of arrival. The citizen files the I-129F showing a real relationship, an intent to marry, and that the two met in person in the last 2 years (with narrow exceptions); after approval the fiance interviews at a consulate. After the wedding the new spouse files for adjustment of status. Children under 21 come on K-2 visas. The alternative is to marry first, abroad or in the US, and file the spouse petition, which is sometimes faster and cheaper.
Education, not legal advice.
Talk to an attorney who does K-1 work