If you are a W-2 employee, any contributions to an HSA account from your gross pay are shown in box 12 with code R, FF, or code W, depending on the type of plan. For an HSA it would be code W. The amount reported in box 12 using any of those codes is not included in box 1 of your W-2. So you can't deduct it again, as that would be double-dipping.
If you are self-employed or have something else that is eligible for favorable tax treatment then it's covered in IRS Publication 969 at https://www.irs.gov/pub/irs-pdf/p969.pdf
