When you first start you will be shadowing an instructor and helping them while you go through a series of new hire clinics to get you to the point where you can start taking groups out yourself. At least until they get too busy and have to pull you to take a group before you think you are ready. Enjoy the training part as much as possible because that may be the time you do the most free skiing all season!
After you get to the point that you are teaching on your own your typical day might go like this: Show up at the mountain early morning and take one run on a green so you can make line up on time, teach groups all day on green runs, with a short break for lunch, take a required clinic after lunch and stand around on a green run arguing about the best angle of the skis to snow for a carved turn (don't forget your protractor) , teach some more groups, go home immediately after teaching with no free skiing because you have to be at your bartender job soon and you are just dog tired.
First thing at the interview is to say "You call yourself a pro? I'm way better than you". Then tell them how you are the best skier on the mountain & that you are gonna rip the shit out of every imaginable line there. After you are hired at the top of the pay scale & get a bunch of free equipment, you will spend the rest of the season cutting lines & shredding pow with the hottest babes you could imagine. They will take you home every night, feed you, get you drunk & have their way with you.
The reality lies somewhere between these two posts, but closer to MattL's. You will get out of it, what you put into it.