The difference between wine grapes and regular grapes is the variety. If you’ve ever heard names like Pinot Noir or Chardonnay, those are not only the type of wine, but also the variety of grape. Those grapes are also typically not very edible. For edible grapes I imagine it works similar to other food production. The farmer sells it to a distributor who in turn sells it to wholesalers who then sell it to stores, factories, etc. Or sometimes the farmer might have a direct contract with a large grocery chain.