What happens after a seller submits the sell form?

Sellers see a Submission received! screen saying you will review their item and reach out by email with an offer. From there they can submit another item without typing their contact details again.

They also get a confirmation email they can reply to with questions, and you get an email notification with the submission.

Every sell form submission is a manual quote request. Review it in Offers in your admin, then send your offer. See How do I respond to a customer’s manual quote request?