How do I use an Allen wrench?

An Allen wrench, or "hex key" is tool used to turn Allen screws or bolts. They come in various sizes, both SAE and metric, and may be single, or foldable into little sets that look like Swiss Army Knives. The heads are far more unlikely to strip out than Phillips or slotted screws, and are often used in, and included with "assemble it yourself" furniture like Ikea stuff. You just insert the end in the screw and turn. Lefty-loosey-Righty-tighty.