to use inventory you have to have the QBO Plus plan (or any desktop version)
inventory items in QB are unique, there is no matrix inventory, so if you stock 7 sizes, then you need an inventory item for each size.
widget - size 1
widget - size 2
etc
You enter a purchase, list each item, the qty you buy, and the total amount for that item
that stocks the item with cost and qty
then you use that item on an invoice or sales receipt to sell it
