If you don't know what you're doing then don't!
Practice, A LOT, on stainless spoons, knives, forks, etc., a good source would be thrift shops, before you ever go near a gun. I can't tell you the number of threads that begin with a cry for help: rollmarks, engraving, serial numbers partially or completely obliterated by overzealous polishing. Things like that can affect the value of the piece you are working on. If you must work on guns see if you can find some hurt units, parts and pieces at guns shows to practice on. If you can't find a local gunsmith to get some instruction try a community college, clockmaker or jeweler.