Your income is not all taxed at the same rate. For example, look at the chart of tax brackets at the link that ee-ea posted. If your filing status is Single, the first $10,275 of your taxable income will be taxed at 10% (for 2022). The next $31,500 will be taxed at 12%, and so on. Those are the tax "brackets." When people talk about what tax bracket they are in, they mean the bracket that the highest portion of their income falls in.
It gets more complicated if you have qualified dividends or long-term capital gain, because there is a different set of brackets, with lower rates, for those types of income.