If you're not importing your Cost of Good Sold automatically as expense transactions importing with one of your linked accounts, you can manually enter them into the "Expenses" ledger.
Just click the Expense tab and then click the "+ Add Transaction" button. Enter the date, vendor, category (be sure to use "Cost of Goods Sold"), amount and a description (optional), and click Save.
Note: GoDaddy Bookkeeping will show you the total COGS amount on GoDaddy Bookkeeping's Schedule C worksheet (and the "Your Spending" reports) based on the all expenditures you have categorized as COGS for the year. However, you may need to reduce your COGS amount for the tax forms, for things like unsold inventory. See Schedule C Part III to determine specific adjustments for COGS.