Why can you see through some objects but not others?

Quite simply, the ability to see through some objects is (usually) the result of the object being what one would call transparent. Light passes through it with little or no attenuation or distortion. A sheet of window glass is just such an object. Light passes directly (pretty much) through it and we see what is on the other side with no difficulty. A brick wall, by contrast, blocks light that is radiated or reflected onto it. A viewer on the other side cannot see "through" it because any light falling on the wall is prevented from passing through to a viewer on the other side.