Hi, and welcome to the forum.

OK, with a K-1 visa (the so-called fiancé visa) you will have to get married within 90 days of your arrival in the US. The other "trick" is that your partner in the US must be a US citizen. There is considerably more detail on the process here: Nonimmigrant Visa for a Fiance(e) (K-1) on the US State Dept. site.
Cheers,
Bev