how do I report my sales from ebay or poshmark and deduct the cost I paid for item? Its showing as gross sales

[DawnC]

You will enter your income in the Self Employment section, then deduct your costs as expenses, all on Schedule C.   Where do I enter Schedule C?

You can enter an expense for the cost of the items.    If you keep an inventory, you can use the Inventory account (Cost of Goods Sold or COGS) in TurboTax.   But you are probably not required to keep inventory, so you can enter your purchases as Supplies.   The article below has instructions for each method depending on the version you are using.  

How do I report Inventory / COGS in TurboTax?