The United States uses a progressive tax system, which means different portions of your income are taxed at different rates. Generally speaking, you pay a higher overall tax rate if you have a higher taxable income.
Tax brackets are the physical representation of this system and show how much you have to pay at various income levels. Since tax brackets and rates periodically change, you should check to see if you are using accurate tables when filing your taxes.
If you use TurboTax to prepare your taxes, you can be sure it is always up to date with the latest tax laws and tax rates.