If my employer also contributes to my 401k, can I use the combined amount of my own & my employer on my tax return or only the amount that i personally contribute?

Use it for what?   If you have a 401k plan at work, the amount you enter into your tax return is on your W-2.  You do not enter it anywhere else on your tax return.  You simply enter all of the boxes on the W-2 just as they appear.

Nothing from your 401(k) summary statement is to be entered into TurboTax.  Anything related to your 401(k) is entered via the entry of your W-2 onto TurboTax's W-2 form.  Your employer, not you, gets the deduction for employer contributions to your 401(k).