Select a kitchen location first (Vendors are stored per location). Then go to Settings > Kitchen Settings > Vendors (/admin/vendors), click Add new, enter the Name and keep Is Active? on, then Save. The list shows Active and Inactive tabs. Vendors are later assigned on meal recipes and used by the Meals by Vendor sales report. The page requires the Vendors module and the List/Edit Vendors permissions; without an active location you are sent back to the dashboard.