You'll be contacted by NVC to start processing paperwork - payment of immigrant visa fee, I-864 fee, I-864 forms and accompanying documents, other documents needed (birth certificate, marriage/divorce/death certificate as applicable, court/police certificates).
Here's a handy steps process starting with NVC (step 2): https://travel.state.gov/content/travel/en/us-visas/immigrate/the-immigrant-visa-process/step-1-submit-a-petition/step-2-begin-nvc-processing.html