Copper cannot be cut with an O-A torch since it contains no iron. Iron in steel is oxidized very rapidly because of the reaction with Oxygen when it is heated to melt point, allowing cutting to occur.

The method you may have seen was called plasma cutting. Equipment to do this is not cheap. One site I looked at had a setup priced around a thousand bucks.

GG

Harbor Freight carries a less expensive plasma cutting unit. I think it's normally about $800, but sometimes goes on sale for about $600 or less. It's probably not a real powerful unit but for sheet metal it may be fine for your purposes. It's easier than oxy/gas cutting but will still require some practice to get a smooth edge.