How to use auth codes

What exactly is an auth, and how do I use it? Because people talk about them all the time. Not really begging, but if someone could help, please, help.

You basically need an auth code. Without it you won't be able to run the program. They're pretty cheap.

P.s I bought an agility bot and I got banned for it xD and it's been a year. Hopefully i get manual unban in the future.