They look like big scissors and work the same way.
Cutting copper sheet with a torch.
Cutting slower will also give you plenty of opportunity to blow away the bits and pieces of copper and dust caused by the cutting process.
Mark the required dimensions on the surface of the sheet using marking tool and straightedge.
Begin cut with metal cutting sheer.
Once the copper sheet has been marked where it needs to be cut the sheers blades are positioned on each side of the sheet as would be regular scissors when cutting paper.
The sheers handles are brought together to cut through the sheet.
Work gloves must be worn during the cutting process as the cutting edge of the copper is very sharp.
Elevate and support one edge of sheet with free hand allowing entry point for cut enough clearance for metal cutting sheer to proceed.
Measure the dimensions needed with tape measure.
For higher gauges meaning thinner copper you can easily do it with standard hardware store metal snips.
Take your time and let the cutter work its way through the copper for a straighter and even cut.