You said, "the flint is under the gun". It is not a flintlock. It is a percussion.
Nice, collectable gun, probably from about the middle 1800's, but as has been mentioned do not try to clean or polish it. That could destroy its value to a collector.
With the stock damage I doubt it is shootable.
Always with these old muzzleloading guns, you should check to be sure it is not loaded. Some of these guns, even a couple hundred years old, are still loaded and could still go off. On yours's the ramrod appears to be missing, but you can take any long stick or a dowel that will easily fit down the bore to check for a load. Just push the ramrod/stick/dowel down the bore starting at the muzzle. Where it stops, mark the stick where it extends out of the muzzle. Then, take the stick and lay it alongside the barrel, on the outside, with the mark you just made being right there at the muzzle end of the barrel. If the stick extends all the way back to the breech, just behind the nipple, then the gun is not loaded. If, however, the stick doesn't reach that far, then it may be loaded or otherwise have some obstruction in the barrel.