An elastic band is made of a kind of plasticky rubber, and is usually brown, the same kind of brown that brown paper packages tied up with string often come in, but other colours are available.
Elastic bands are traditionally used to keep plastic bags closed, or to hold together bundles of paper money, or something like that, but were quickly discovered to be a basic, dangerous, hand-held surface-to-air or surface-to-surface ranged weapon. Elastic bands are the first lethal weapons that children learn to use, and with deadly efficiency do they do so. Suicidally, most major world governments do not consider the rubber band as a threat to international security, and the possession of elastic bands or elastic band-making equipment is legal.
The best way to fire an elastic band is to wrap one end of the loop around your thumbnail, and pull the other back to be level with your thumb-joint, where you can load your ammunition, from among the following suggestions:
Bits of mashed up paper make a lovely sort of satisfying splat.
Bits of chocolate, which will be a nice surprise for your target.
You may find the best types of elastic bands in industry: the great big thick ones. They are usually a couple of inches thick, and are really springy, and are perfect for firing tennis balls with.
The correct method for firing anything at someone is to sneak up behind them with the rubber band primed in the aforementioned manner, fire it and run away very quickly. Your target will likely be rightly miffed, so make sure that you have your escape route planned and have checked it well in advance, or you may well receive a nasty look from your victim.
Happy ballistic missile flinging! Poioioioioioinnnggggggg!!!!