This is the 268th most frequent Czech word.
auto
Car.
In this usage, 'auto' refers to a 'car' as a noun, indicating a particular object.
To auto je nové a červené.
That car is new and red.
Here, 'auto' functions as a possessive noun, denoting 'my car' and showing ownership.
Mám rád své auto, protože je spolehlivé.
I like my car because it is reliable.
In this sentence, 'autem' is the instrumental case of 'auto', indicating the means of transportation used for the trip.