The Autodoc booth scans your body and heals injuries like cuts, for a fee. Just select the wound(s) you want treated (i.e. all of them, unless you're really broke). It will restore part of your health bar, but not all. The rest simply takes time.
Autodocs can rescue your life, because "critical wounds", other than just "injuries", never heal on their own and will kill you if not treated in time. (You can see with the 'E' key if you have any.)
Some Autodocs aren't booths but fancy looking hospital buildings, but that's just decoration, the result is the same.