Sorry, I misunderstood. You are trying to ADD new inventory into your warehouse? Then you need to use either a oInventoryGenEntry object (OIGN table For "Goods Receipt" for something that was transferred to you from another warehouse, or a new product you made or something you found lying around), or a oPurchaseDeliveryNotes object (OPDN table for "Goods Receipt PO" for something that you purchased from a vendor with a Purchase Order) to add the item to the warehouse.
There may be other objects to add to your inventory, but those are the only two I know about. Now if you want to QUERY the current warehouse inventory and level, then you would use the ItemWarehouseInfo object, which is a child object of the oItem object.
I hope this helps.