For good, for ill, or for neither, firearms are an integral part of American life. Everyone knows in a general sense what guns are, but not so many know much more than that. The conventional wisdom is that those of us on the left are less familiar with firearms than those on the right (a premise with which I do not agree), but the fact is that it important to have a basic understanding of how firearms work.
At the most basic, a firearm is a device used to deliver a projectile, usually at a high rate of speed, towards some sort of target using chemical propellants that are NOT carried onboard the projectile. Firearms have evolved over the centuries from quite crude affairs to the highly sophisticated devices that are available currently.