Well, if you hold it close enough to the computer.......Sorry- just kidding. I think you mean how do YOU tell what gun YOU have. Let's start with the obvious- long gun or handgun? Next, what markings...
Depends on which gun. By opening the action, and being able to see that there is no cartridge in the gun is the basic method. Some guns require removal of the magazine first. A muzzleloading gun,...
generally you can establish the "power" of a weapon by its caliber this works great with small arms, once you get in to bigger guns ie artillery and ships guns there is more to it then just caliber....