Inventoria works with barcode scanners in "HID keyboard emulation" mode. Basically, it acts like a second keyboard. The advantage of this is that you don't have to worry about specific drivers. Once you scan an item and you sell it, it will automatically updated your inventory.
In order to add an item, you need to go to "Add new item", the cursor in the "Item Code" should be blinking, now you can star scanning the items.