What does it mean to become an Apprentice?

Hi everyone,
Just a quick question: What does it mean to become an Apprentice (or Expert or Master, for that matter) in a certain skill? At first I thought this is another way to improve your skills: instead of spending character points, you pay someone to train you. But now I guess that's not it, because after becoming an apprentice in, say, Persuasion, I still have only one point in it. So, my question again, what good does becoming an Apprentice (or Expert and Master) do?
Thank you for your replies

 

You get a perk, specific to the skill. See the manual for the full list.

 

Thanks a lot!