You've been given a great opportunity, OP! Not every stable will take a complete horse newbie (and I mean that in the nicest way possible. You're going to have so much fun!) to work for lessons.
I second the advice to never stand idle. That is my BOs biggest pet peeve and she'll really tan your hide if she finds you lollygagging. I work at a farm in exchange for personal ride time on their horses, use of their cart, and and a discount for boarding my horse, and I'm busy 110% of the time. I started out just like you with no real experience with horses, so I'll give you my experience as well as some advice that I've found helpful.
One big thing that helped them even CONSIDER me was my book knowledge of horses. While I hadn't had any real experience with horses, I knew basic horse colors, anatomy, genders, how to measure their height, basic care (theoretically at least), different types of tools for grooming/cleaning/tacking and what they are used for, a few major breeds, etc. They'll most likely teach you this as you go along but it will not only show them how much you want this, it shows them that you're already working hard to learn. Just don't sound like a know it all. Don't go around listing things just because you know them. Ask intuitive questions, be a good listener, remember what they tell you, and if they ask you something that you already know, don't be afraid to answer them. My BO loved that I already knew all of this information because it made it easier on them when they were teaching me. Remember though, book knowledge and experience are two different things!
When I first started working at the farm, my basic jobs were to clean the pasture and stalls (as well as rabbit kennels/turkey pen but I'm sure you don't have that! ICK), scrub water troughs and buckets, clean tack, sweep, and re-set barrels, poles, etc during other people's lessons. As I got more experienced I was allowed to help rug and fly mask the horses, turn them out and bring them in, tack them for lessons, teach kinds to tack the horses, and feed.
I've been at the farm now for 4 1/2 years, and now I have just about every job you can think of xD I do all of the chores that I first mentioned (though I don't do much mucking anymore. The newbies get to do that because I'm too busy!) and I also help tune up the lesson horses, exercise the ranch horses, run birthday parties as the hostess, do basic medical care on horses that just have a scratch or something, bathe, assist with lessons, repair fences, and a few other things. I can't tell you if you'll ever have those kinds of responsibilities though. I'm only 16 so I feel VERY priviledged to have all of the jobs that I do. I'm also the head of our therapy program and am in charge of most of our horse's nutrition and worming scheduals. It gets pretty crazy!
One thing that I would of wanted to know when I first started that I didn't know though? Its EXTREMELY addicting! LOL. I now have 2 horses and am out at the barn every moment that I get, even when I'm not working!
Everyone in your life is meant to
be in your journey, but not all of
them are meant to stay till the end.