Where do I put my cost of items? I sell on eBay and the postage it takes to send the items.?

You will need to add expenses.  For costumes you purchased to sell, you will enter these in inventory.  For postage, you can choose "other miscellaneous expenses" and add the description "Postage."

Here is how to do this in TurboTax Online:

• Log back in, navigate to Federal > Wages & Income > Self-employment income and expenses > Add/Edit
• Find your business and choose "Edit"
• Now, adjust your income or expenses as needed

If you are using Desktop:

• Navigate to Federal Taxes > Wages & Income > Business Items > Businesses Income and Expenses (Sch C) > Update
• Find your business and choose "Edit"
• Now, adjust your income or expenses as needed