It depends.  If it is listed in Box 12 with a code W, then these are pre-tax contributions.  While these contributions are your employee elective contributions, they are payroll contributions because you received the tax benefit by having a lower taxable income reported on your W-2.

TurboTax will carry this number over to the correct form, Form 8889, where it will appear in the box of Employer Contributions.  They are only called that because they are pre-tax contributions.  You will answer a few questions about if you had qualifying HSA coverage for that year, and you may report any medical payments you made with your HSA as well (which are reported to you on a Form 1099-SA if you had any).  As long as you were within your limits, however, none of this is taxable, but the IRS does require it to be reported.