A draw file has a single angled cutting edge to its teeth. It is used to cut across surfaces.
You hold the file in both hands, with each hand on the file itself, rather than on the handle. The hands are separated just enough to allow the workpiece to fit between them. Some files cut when drawn towards you; other when pushed away from you. Determine which yours is on scrap. Take only one stroke per placement of the file. Then move the file in your hands, reset the file on the barrel, and take the next stroke. This allows you to use the entire file evenly, and then you can flip it over and use the other side, if needed, before you need to card the file to remove the filings that will undoubtedly be clogging the file. Card carefully, and inspect the teeth with good light. a copper pick is often needed to manually pluck out really stuck filings from the teeth Its important to remove the filings so they don't scratch or score your workpiece on the next stroke.
Many crafstmen will fill the teeth of their files with chalk before using them, in order to lubricate the teeth, and keep the filings from sticking so they have to use a pick to clear the stuck filings. Chalk does work.
You can buy it in one form or another at most hardware and home supply stores- where you buy your files. Buy the best quality files you can find. Stick with American made Nicholson files, if you can. The Chinese stuff does not have a very good reputation.
When filing the muzzle to change the POI, put pressure on the side of the muzzle that needs to be filed. You can always clean up the rest of the muzzle after you have moved the POI to where you want it, by filing a complete flat bevel across the muzzle.
The only time you may have to use a file other than a draw file( single cut) is on a double barrel shotgun, where the two barrels are shooting away from each other. Then, a half round file may be needed to remove metal where the two barrels are joined, to bring the POIs back together. This is often seen to have been done to original double barrel shotguns, and I have seen many such guns in the used gun racks at Friendship.