An approved I-130 only means that USCIS thinks you are really married; you still have to establish that the non-US Citizen is eligible for a visa. The Immigrant Visa Application stage in the process seeks to determine whether any would-be immigrants ought not be allowed to proceed to the US. Put another way, the I-130 petition stage is about the US Citizen anchor relative proving relationship, while the visa application stage is about the would-be immigrant proving identity and admissibility.
The immigrant visa application process begins with assignment of a visa application ID number and invoice for the application fee, issued by the NVC. USCIS transmits notification to NVC of approved electronically filed I-130 petitions upon approval, so case creation by NVC typically takes no more than a few days (if not a few hours) from USCIS approval. Steps in NVC Processing are described on their website. NVC coordinates preparation of the immigrant visa case for the US Embassy where the immigrant visa interview will take place. Current NVC Timeframes are posted on their website.
The Consular Electronic Application Center (CEAC) is the gateway to all US visa applications. The immigrant visa application is the DS-260, an online application form that gathers comprehensive biographic information about the visa applicant. The DS-260 lives in CEAC, which is also where payment of the initial immigrant visa application fee and affidavit of support fees can be paid (n.b. payment must be from a US bank account).
Long form birth certificate (showing names of both parents)
Police Certificate for each country in which you resided for 12 months or more since the age of 16
Marriage certificate
Proof of termination of any prior marriages (for both)
Medical records, including vaccination history: the immigrant must submit to a full medical exam by an authorized physician (panel physician)
Proof of financial support (in most cases)--See "Can You Afford This"
The US spouse must provide an Affidavit of Support, including information from the past 3 years of US tax returns and a complete copy of the most recent tax return (or an IRS tax transcript)
If employed in the US, the US spouse must show proof of employment
If relying on income of the the immigrating spouse, proof of his/her earnings
If relying on assets, proof of assets
In some cases additional documentation may be required, such as military discharge
The US Immigration and Nationality Act enumerates several basis upon which a consular officer (or airport inspector) can deny an individual admission to the United States. These include: medical reasons (such as infection with a highly infectious disease or failure to be properly vaccinated for certain diseases); dangers to public safety; past criminal records; and past violations of US immigration laws. Additional information regarding inadmissibilities can be found in the Inadmissibility article in this website. To determine whether an applicant may be inadmissible, the visa application stage requires completion of Form DS-260; a medical examination, including proof of required vaccinations; and police clearances. The application process culminates with an in-person interview with a Consular Officer at the US Embassy.