The US Tax system is a progressive tax system, which means you do not pay a flat tax.
Instead, your income fills up various tax brackets and as your income crosses different thresholds you move to a new tax bracket. This allows you to have two important tax rates: Marginal Tax Rate & Effective Tax Rates
Your marginal tax rate is typically the percentage of taxes you will pay on your next dollar.
Your effective tax rate is the total amount of your taxes paid divided by your GROSS income. You may be surprised at how low your effective tax rate is.