Tin snips are much like shears, except they are designed to cut thin metal surfaces like sheet metal. If you are inexperienced with tin snips, be prepared for stiff cast-offs, which are often sharp and don't clear away easily. You may need to wear gloves while learning how to properly use your snips to avoid getting stabbed by a sharp corner or sliced by a jagged edge. Until you get used to using the snips, you will most likely create a jagged edge or two, so practice on a piece of junk sheet metal until you get the technique down pat. This will minimize your margin for error when working on the actual project.