Cost of inventory, where do i add my purchases as expenses that i used for inventory?

[JulieCo]

You will want to add this amount in the Inventory/Cost of Goods Sold business expense entry section of TurboTax.  See sample screenshots below for either TurboTax Self Employed or TurboTax Home & Business.

If you do not track inventory, then just enter $0 as the beginning and ending inventory balance, plus enter your inventory purchases for the year and then TurboTax will use that for the Cost of Goods Sold amount on your Schedule C in your tax return.