To see something, light has to enter the eye. The sun, lamps, lasers all emit (send out) their own light (they are luminous) however, most objects are non-luminous you can only see them because of day light that bounces of them. They reflect light and some of that light enters your eyes.
The only reason you can read this page is because the light bouncing off of it. The white parts of this page reflect most light whereas the black letters absorb almost all of the light that strikes them making them look dark.
Most surfaces are uneven, or contain particles that scatter light. As a result, the reflect light in all directions. This reflection is diffuse. However, mirrors are smooth and shiny. When they reflect, the reflection is regular.
Transparent materials like glass and water let water let light pass right through them. They transmit light.
