So, Aperture, Shutter and ISO.
We know what they do. But when and why do we use them?
Portrait (Face is in focus, background isn't): Large Aperture (low f-number)
Landscape (Everything from foreground to background is in focus): Small Aperture (high f-number)
Running Athlete (To capture action): Fast Shutter (1/500th of a second to 1/4000th)
Starry Night (No lights, very dark): Long Shutter (1/50th of a second to 30 seconds)
For now we are leaving the ISO at 100.
The first two use the Aperture control to set your exposure. Set camera to A or AV, move the dial so the aperture value goes all the way up or down. The camera will look at available light, and where the ISO is set, and give you the Shutter speed you need for a correct exposure. The second two are controlled with the S or TV dial.
If, for instance, you want to shoot a beautiful landscape of your back yard. Set the Aperture to f-22, point the camera and hit the shutter half way. The camera will meter the light and determine what speed shutter it needs to give you that aperture. Remember, though, that the small aperture allows less light, so the camera may give you a shutter speed of 1/100th of a second. The sad news is, there is no way you can hand hold the camera that long without even a little blur. So, adjust your ISO to the next level. At 200, the shutter may move to 1/250 of a second. Better, but not great. 400? Hand-holdable*, but it now starts to get grainy.
All these factors are determined by the capabilities of your camera. VERY roughly speaking, the newer (and the more expensive) your DSLR, the better it will be at this.
There are other ways to overcome these obstacles, and but they will be covered a bit later. For now, we can live with a little graininess. That back yard will be there for future, better shots.
Homework? Hug your kids.
*My blog - my made up words!