how does one audition to be a actor?

That's not how it works.
First, you have to have huge talent, determination, a great imagination and high intelligence.

Then you're going to need training and experience.  Typically, that takes at least seven years, training to degree standard and performing regularly with a good amateur theatre company, doing student films, short films and indies, etc.

Then you need to get signed by a good, genuine agency.
The agency then tries to find you suitable auditions for TV, movies and stage plays.
If they identify any roles for which their connected production companies are holding auditions, and put your name forward if you're interested.

If the company likes the look of your resume/CV, they'll invite you to attend an audition.  It's then up to you to convince them that you're the best actor for that role.

I hope that helps you to understand!

You can check the website for the show/TV station to see if they are holding an audition 

take acting classes

go to the networks agency you want to audition with