Payments you receive are gross income. The goods you arrange to be shipped are an expense. Your shipping cost is another expense, as are credit card transaction fees. If you have a business-only computer, cell phone, printer or landline, you can probably deduct it as an expense as well. (Although, if you stop using the equipment for business, you may have to repay some of that deductions.)
You owe self-employment tax (15%) on your net profit from business. This is the self-employed person's version of social security and medicare tax. Your net profit also flows onto your personal tax return where it is combined with any other income from other jobs, and the effects of your deductions and credits is taken into effect.
Because you don't have withholding, you probably need to make estimated payments to the IRS 4 times per year so as not to owe penalties for late or underpayment of your taxes.
You may want to look at the Quickbooks self-employment bundle which includes a single-business version of Quickbooks for your business records and a single-business version of Turbotax for your tax returns.
