Wow, how about starting with something simpler like how come the Leafs suck? But, I understand that I do have a job to do, Gary...
The reason you can see through glass basically is that there is no reason that you can’t.
Despite its appearance, glass is a highly viscous liquid rather than a solid, and you can see through it for the same reasons that you can see through water.
Coming up with such an admirably simple answer, Mr. Brun, allow me to expand a bit further. You are welcome to get your teacher, friends or family to write me further should this not make much sense to you.
Most liquids, when cooled, have a freezing point at which they suddenly become solid. Glass, by contrast, simply gets gradually stiffer as it cools. At room temperature its rate of flow is so slow that it would take billions of years to ooze out of shape, and for most practical purposes it may be treated as a solid. Its internal structure, though, is not the regular crystalline latticework of your standard solid, but rather is basically random, like the typical liquid. As with many liquids, the rather loosely spaced molecules in glass are simply not big enough to obstruct the passage of light particles (see my paper on the properties of glass here).
Furthermore, (a) there are no footloose electrons in glass to reflect light, as with metals; (b) the energy levels of the individual atoms in glass are not such that they absorb light in the visible spectrum, although they will absorb infrared and ultraviolet; and (c) there are no internal boundaries or discontinuities in glass as there are in ordinary crystal solids to refract light, which would cause some light to be lost to internal reflection. (Glass reflects light only at its external boundaries-- that is, the boundary between the glass and the surrounding air, or whatever. This permits refraction to be precisely controlled, which is what makes eyeglasses, and optics in general, possible). In short, the reason you can see through glass is that there is no reason for you not to be able to see through it.
That is all...