To make a stained glass first you need to practice cutting the glass in straight lines and curves from glass to acquire the hack and the confidence that make it look easy.
Glass cutting actually quite an easy process and only required a few tools. It has nothing to do with strength. All you need is to master the technique. Always observe safety in doing glass cutting and keep children away while doing it.
The most essential tool is a glass cutter. Avoid cutters with more than one blade as they can be awkward to handle. Buy the best quality you can afford if you intend doing a lot of glass cutting.
The cutter has a hard steel wheel which score the surface of the glass and when pressure is applied to the reverse side of the glass, a fracture or run will allow the glass to be broken off in the desired shape.