If you need to drill a hole in glass, here are a couple tips:

1 - Submerge the glass and bit under water. This will keep the bit cool and it will reduce the amount of glass flying around. Be sure to still wear safety glasses. And make sure just the drill bit and the glass are under the water, do not let your drill get in the water or you could get electrocuted.

2 - Use a diamond-tipped drill bit. It is nearly impossible to drill through glass with any other type of drill bit and even if you do manage to do so, the resulting hole will be ragged. Diamond-tipped bits are rather expensive, but they are the only way to go if you are drilling in glass.