Don't know what the $325 is for. Is that a credit on your return? What line is it on?
The 12,200 is the Standard Deduction Deduction for Single. Everyone gets that. It's a good thing. You get to subtract either the Standard Deduction or all your Itemized Deductions whichever is more. It is subtracted off your income before the tax is calculated so you get taxed on a lower amount. Which means the first 12,200 Single or 24,400 Joint of your income is not taxed and is tax free.