An automobile.

"My brother is an auto mechanic."

A setting for automatic operation.

"Put it on auto."

An automatic gearbox / transmission.

"A body coloured centre pillar signalled the arrival of an electronic four-speed auto, slight suspension revisions and minor trim changes."

A car with an automatic gearbox / transmission.

"It wasn't too bad but we did hire an auto (couldn't imagine changing gears with my right hand)."

To travel by automobile.

An autorickshaw.

"... users are often unable to note down the number of the taxi or the auto as the driver will just zoom past."