Glass is one of the most difficult materials to cut or make holes in because it shatters and cracks so easily; however, there are ways to drill through glass if you have the right kind of drill bit.
In general, two types of drill bits can be successfully used on glass: tungsten carbide spear-tipped drill bits and diamond-tipped drill bits; there are also diamond-coated drill bits. Carbide-tipped drill bits are most commonly used for non-tempered glass, ceramics and tiles. The tip is a tiny spade-shaped point made of super-hard tungsten carbide, which is extremely durable and can withstand the friction of drilling into glass. Diamond or diamond-coated drill bits are even harder, and many people prefer them for working with glass and other hard but fragile materials. For specialized jobs such as cutting holes for pipes through a window or mirror, there are tube-shaped drill bits with a diamond coating along the cutting edge.
Whichever type of drill is used, it's important to work carefully and safely. You should wear gloves and protective eyewear so that you won't be cut by any glass shards that break off. You will need some kind of liquid to lubricate the drilling process and to keep the drill bit from overheating. It can be hard to start your hole in exactly the right spot, as the drill may bounce off the glass until it has ground away an indentation. One way around this problem is to mark the drilling spot with a pen or pencil and then put clear tape over the area. Not only will you see the place clearly, the tape will help provide the initial friction to start the drilling process. Keep up a steady pressure with the drill and remove the drill at a relatively low speed. Do not use a hammer type of drill.