General:
* Autobiography: A written account of a person's life written by that person.
* Autoimmune: Relating to an immune response directed against the body's own tissues.
* Automatic: Happening or done without conscious thought or effort.
* Automation: The use of machines to perform tasks that were previously done by humans.
* Autopsy: A postmortem examination to determine the cause of death.
* Autonomy: The right or condition of self-government, especially in a particular sphere.
More specific:
* Autoclave: An apparatus for sterilizing by means of steam under pressure.
* Autocrat: A ruler who has absolute power.
* Autograph: A person's own signature.
* Autoignition: The ignition of a fuel-air mixture by heat alone.
* Autolysis: The destruction of cells or tissues by their own enzymes.
* Automata: Machines that are able to act independently.
* Automata theory: A branch of computer science that studies abstract machines and their computational capabilities.
Less common:
* Autoeroticism: Sexual stimulation of oneself.
* Autogenous: Originating within the organism.
* Autokinetic: Relating to the apparent movement of a stationary object when viewed against a dark background.
* Autopsychic: Relating to the mind or personality of oneself.
This is not an exhaustive list, but it gives you a good starting point for understanding how the prefix "auto" is used in English words.