Let's quickly get some of the boring facts out of the way. The Annapurnas are a bunch of mountains in the Himalaya, a lot of them higher than 7000m, the highest being Annapurna I at 8091m. As a point of reference Mt Everest (or Sagarmartha as its known in Nepal) is 8848m, Mt Kosciuszko (the highest mountain in Oz) a mere 2228m. Simply speaking, the Annapurna Circuit trek takes you around this group of mountains by following a river (namely the Marsyangdi Khola) along one side of the range, steadily gaining altitude, culminating in the crossing of Thorung La (a mountain pass at 5416m), and then following another river (the Kali Gandaki) to finish near the lakeside town of Pokhara. The trek is roughly 300km long, depending on where you start and finish, and can take anywhere between two and three weeks.
As the trek runs along old trade routes between Nepal and Tibet, there's villages and thus guesthouses all along the way, so there is no need to carry your own food (not even for lunch) or a tent. However, as a lot of the lodges only provide beds without blankets, it is still necessary to carry a warm sleeping bag, especially for those cold nights above 3000m. Add to that some thermal underwear, a thick downjacket and maybe a chunky book for quiet evenings, and you're still looking at a reasonably heavy backpack. Mine certainly was, and being stubborn and proud, I insisted on lugging it around myself, instead of getting a porter, which a lot of trekkers understandably do. Meanwhile, my guide Kabi was skipping along with nothing more than a daypack, which inexplicably contained everything he needed.
On the subject of guides, the Annapurna Circuit is the most popular trekking route in Nepal and as such, it is fairly easy to find your way and meet other trekkers along the way. The trek for the most part isn't really technically difficult, so as long as you got the right gear and follow the rules for avoiding altitude sickness (we'll get to this later), you should really be fine. Even if you do hurt yourself chances are another hiker or local will be along soon enough. What I'm getting at is that if you can read a map you don't necessarily need a guide. Having said all that, a good guide can give you insight into local culture, that you might otherwise miss out on. (Plus getting a guide helps in assuaging your parents worries about you going for a walk among the highest mountains on earth.)