Aperture is a very neat function of an SLR/DSLR. The aperture is located inside of the lens and ranges from f/1.2 to typically f/32. The lower the number the bigger the opening and the greater the number the smaller the opening. The aperture setting f/1.2 will let the most light into the photograph and f/32 will let the least amount of light in. The best way to explain aperture is to take your hand and make a circle and look at the light through the circle. now make a very tiny circle with your hands and look at the light. Is there a different amount of light coming through the circles? The big circle you made is f/1.2 and the tiny circle you made is f/32. This is the same thing your camera does. It has a mechanism in the middle of your lens that creates a big or small circle that controls the light that comes into the lens. Aperture also controls what is in focus and what is not in the background. This is better called depth of field which we will go more in depth on next week.
The f/ means f stop which means the fraction of light you are letting touch the sensor/film.
Below are two photographs. One the background is not very clear (lower f/stop) and one it is clear (higher f/stop).
