Okay, metoe. I'm a firm believer that there's no such thing as a "stupid" question. I'll try to give you the basics.
An AR-15 is the semi-automatic rifle that the US M16/M4 and Canadian C7/C8 families are based on. I'm sure that you've seen lots on TV/Movies/Games. Most are chambered for NATO standard 5.56X45mm, but will also fire .223 Remington ammo without a hiccup.
Anything in the AR family (and there are lots of different manufacturers and models) is restricted here in Canada. It is restricted "by name", which means that anything based on this family is going to be restricted - nothing that we can do in terms of modification is going to make it non-restricted. This means that it can only be fired at an "approved" range which permits it. No firing at the gravel pit next to your buddy's uncle's girlfriend's property unless you want to get very well acquainted with the Surete! (no accents on this keyboard)
Quick caveat here: The AR-180B is a different animal. It doesn't share many parts, and it has a different operating principle. That's why it's not restricted.
In general, an AR-15 is a lot of fun at the range. For the money, they are relatively accurate, relatively reliable, and very customizable. Ammo is relatively cheap too.
There are folks that love to hate the AR-15 family, and there are folks that are firmly convinced that the AR-15 family is the best thing to hit small arms technology since the pointed stick. There are also LOTS of folks (myself included) that fall somewhere in between the two camps and enjoy owning one. A big part of this enjoyment comes from the fact that you can buy parts for your rifle and customize it so that it looks nothing like it did when you bought it.
If you want one, get one. Buy from one of the sponsoring dealers here. TSE, Wolverine, ArmsEast, Freedom Ventures, Questar...they all carry good quality brands of AR (no LMT vs. Stag vs. Bushy pissing contests here please).
If you're not sure if you want one, see if you can find someone in your area willing to let you try theirs out. Offer to provide your own ammo for this (common courtesy if you ask me).
I'm hoping that his has answered your questions, but I have no way of being sure. In the future, making your questions as specific as possible will help people to answer them constructively.