The list
Filters (Item Code, Name, Barcode, created dates) apply when you press Search; 10 per page. Columns show Qty On Hand (the total across all warehouses), unit, reorder point and cost. A Low Stock badge marks an item at or below its reorder point in a warehouse you can see.
Item fields
Item Name, SKU (blank builds one from the pattern in Settings; unique; cannot be changed later), Barcode, Unit of Measure (a name from the Units catalog; there are no unit conversions), Reorder Point, Reorder Qty, Cost and Default Supplier (used to suggest the item on reorder drafts). There is no opening-stock field: stock arrives by receiving a purchase order, a manual inbound, or an adjustment.
Link to a store product ties the item to a product so the store's orders use this stock. Linking is not enough on its own: in the store, set the product's Stock source to "Inventory plugin" (that also creates items automatically for every variation).
The item Cost is used only for the layer cost of a positive adjustment and the price on auto-generated reorder drafts. It does not change the value of stock you already hold.
The item page
Item details, Total Value (remaining layers × cost, all warehouses), per-warehouse Stock Levels (on hand, reserved, available, with Out of Stock and Low Stock badges) and the last 50 Movements. Movement types: Stock In, Sell, Adjust, Transfer In, Transfer Out, Return, Lost, Damaged, and Correction.
Adjust Stock
Adjust Stock takes a warehouse, a non-zero signed whole Delta and a Reason (up to 500 characters). A positive delta adds stock as a new cost layer at the item's Cost. A negative delta consumes layers per the costing strategy and records the average cost taken. You cannot remove more than the layers hold ("Insufficient cost layers available for this operation."), but the check ignores reserved stock, so available can go negative. Manual adjustments post nothing to accounting.
In a warehouse, the Inbound and Outbound dialogs offer Receive (with a unit cost of your choosing), Correction, Sell, Lost, Damaged and Adjust.
Transfer Stock
A transfer moves stock from one warehouse to another: layers are consumed at the source and one new layer, at the average cost, is created at the destination, dated now. It also ignores reserved stock and posts nothing to accounting.
Deleting
Delete is permanent, needs the delete permission, and is refused if the item has any movement, purchase-order line, stock or remaining layer ("This item cannot be deleted because it still has stock or history."). An item that has ever had a movement can never be deleted, even at zero stock.