It depends on how precise a curve you need. Stained glass is made by sketching a pattern on paper first then laying glass on top of it and following the curves freehand with a cutting tool. The more severe the curve the harder it is to cut.
If you need a more precise cut, a tool is used that looks like a compass with a suction cup. If you don't mind a few bad cuts, you can experiment until you can do it (on scraps preferably).