Aperture: Refers to the amount of light that enters the camera. Small aperture means little light is entering the camera. Large aperture means a lot of light is entering the camera.
F-Number (or F-Stop): Also refers to the amount of light that enters the camera. Higher numbers denote less light is entering the camera (i.e., a small aperture). Smaller numbers denote more light is entering the camera (i.e., a large aperture).
For example, at F-22, the lens allows only a small amount of light, and at F-2, the lens allows the maximum amount of light. Each F-number represents a double increase or decrease in the amount of light allowed into the lens. Remember the relationship is inverse (i.e., opposite–when one goes up, the other goes down). On point-and-shoot cameras, you can adjust the F-number with the manual function.
Shutter Speed: Device that controls the exposure time of the photo. The exposure time usually begins at 1/2000 seconds and goes up to 30 seconds. A fast shutter speed is indicated by a smaller amount of exposure time. Thus, a 1/2000 second exposure time is a very quick shutter speed. A 30 second exposure time is a very slow shutter speed. These are some great examples of slow shutter speed photography and fast shutter speed photography.
ISO Speed: ISO speed is the sensitivity of the digital sensor. It is usually expressed with the following numbers: 50 | 100 | 200 | 400 | 800 | 1600 | 3200. These numbers tell you how fast the digital sensor reacts to the light. A small number means that it takes a relatively long time to take a photo, which is helpful in low-light settings and nighttime. Whereas, a large number indicates that is takes a relatively short time to take a photo, which is helpful in sunny conditions.
With point-and-shoot cameras, you don’t really need to worry about the ISO speed, the camera sets it for you. Generally, you want to stay in the low range when you take photos.
Balancing Stops: Since f-numbers and shutter speeds are both measured in stops, keeping balance is easy. If you take away 2 stops from the aperture (f-number), you can give 2 stops back with the shutter speed and end up with the same exposure level.