This has been asked and answered a few times, and the short version is that Hitler acted as a runner - carrying messages between his regimental HQ and battalion HQs (but not the front line) - for most of the war, which, while a dangerous job, did not expose him to combat. There's no evidence he ever killed anyone (other than himself) at any point in his life, although, certainly, he issued plenty of orders that resulted in people's deaths.

Further details can be had from these older threads:

Did Hitler ever personally kill anyone during his lifetime?

Not including his own wife, did Adolf Hitler ever physically kill anyone?