Sathiharu, Here is my experience at the US embassy during my immigrant visa interview. Will go over sponsorship letter requirements, how to dress for an interview, what goes inside the embassy when you go for an interview. See YouTube video's deskription section for 15 actual US Visa Interview questions.
This is after you got the DS-260, completed medical exam, prepared police report, attested police report with Department Of Consular Services at Tripureshwor and other visa important documents such as SLC certificate (10th grade),+2 (12th grade), Birth certificates, etc for DV lottery, Student, tourist and business visas. Documents may vary per visa type.