Create items and sizes with purchase and selling rates. Each variant has its own stock. Existing canteen items are shared, so stock is counted once. A class set lists item quantities at a fixed price or the sum of its items.
Open General → School Shop → Catalogue. Your school administrator grants access in Users & Privileges. Stock changes when a purchase is saved or a sale is completed. Parent orders reserve no stock until delivery. Check the displayed totals before confirming a financial action.