Duster usually refers to one of several types of electronics "compressed air" aerosols. It contains a halogenated hydrocarbon, usually difluoroethane, sometimes tetrafluoroethane.
Please, for the love of God, DON'T START DOING FUCKING DUSTER! It ain't even that fun... hell you can get almost as high breathing into a paper bag. Not only does it cause brain damage, but it's bad for your liver too, and probably your kidneys. Plus it can interfere with your heart rhythm and cause sudden death; around 80 kids a year die this way.
Doing duster on a regular basis is gonna mess you up later down the line... you may not notice it, you could just end up a bit more brain-damaged and stupider than you otherwise would've been. It's not worth it! I assume you are young; just bide your time and you will have a chance to do all sorts of drugs that are actually enjoyable.
Personally I believe it's best to hold off on the heavy drug abuse until at least college... I am very very glad I didn't get involved with anything serious in high school, I really would've been unprepared for it at that age. However, if you're desperate for drugs now and can't get weed or liquor, pick something better than duster... drink some cough syrup, take a bunch of Benadryl, or smoke some nutmeg. None of these are really all that fun, but they're much much better for you than duster, if you insist on doing something.