You need to pay both fees first. After the payments are processed (takes a few days), you need to complete and submit both the DS-260 and the I-864. Once those are submitted, you need to upload all relevant documents, such as police report, birth certificate, proof of income, etc.
All of these need to be done before you case can be submitted for review by the NVC. Just submitting the forms alone will not start the process.
This the stage my wife and I are currently in. The NVC timeline show that as of Oct 31 they were reviewing cases from Sept 8. We submitted everything on Sept 30 so we hope to hear something around Thanksgiving.