The welcome letter will contain your login details to the ceac portal. Once you login, you'll be required to pay some fees $425 if I remember correctly(mind you you can't pay with a credit or debit card, it has to be a savings or checking account). Which will take 3 days or more to process, after which you'll be granted access to fill your ds-260 forms and submit your civil documents. The petitioner on his end will be required to fill and submit an Affidavit of Support, provide his recent tax return or transcripts, and w-2s.
NVC Requirments
Petitioner/Sponsor
1- form I-864 Affidavit of support
2- Tax return transcripts and W2 (most recent)
3- Proof of US Citizenship
4- Proof of Current employment
5- final divorce degree (if applicable to her)
Applicant/Beneficiary civil documents
1- passport data page
2- passport photograph
3- Birth certificate
4- Marriage certificate
5- Police report
6- final divorce degree (if applicable to you