Black powder makes a hell of a bang! These guns were not in use until the fourteen hundreds. They fired a spray of shot, which would do a lot of damage to any groups of enemy soldiers. The arrow was still the main weapon, and until the last century was better than guns at killing people... Oh Good!
The order of firing was: swab down the muzzle with wet rags, dry with another swab, load canister of black powder in the breech, load shot via the muzzle, place fuse in powder and light it. Meanwhile, keep your powder dry and watch out for enemy soldiers rushing through the smoke to kill you and capture the gun.