After you have completed the steps on the Immigrant Visa Process on usvisas.state.gov, including paying the necessary fees and submitting the required immigrant visa application form (DS-160), Affidavit of Support, and supporting documents to the National Visa Center (NVC), they will review your file for completeness. Once your case becomes qualified for an interview, NVC will mail you a letter when it sends your fiancé(e) case to the Embassy to inform you to take the actions to apply for a K-1 visa and prepare for the interview.

You can learn more about the interview process on usvisas.state.gov.