All right, now that we've got the basics of ISO, shutter speed, and aperture down lets get a little more into in what it all means (and if you need a little refresher check it out here!).
So lets start out with EXPOSURE, what exactly does that mean?
Exposure literally mean how much light gets exposed on to the film in the camera, and aperture, shutter speed and ISO all determine that. So a good exposure is when all the elements are working together for the look you are going for.
DEPTH OF FIELD
Depth of field is what is in focus when looking through the lens of your camera. Is the foreground in focus? Is the background in focus? is everything in focus? Depth of field refers to what is sharp and what is blurred. A deep depth of field is when both foreground and background are in focus, and a shallow depth of field refers to on a portion of the frame being in focus.
Your aperture setting can affect your depth of field, the smaller the f/stop the shallower the depth of field (remember from lesson 2?), and the larger the f/stop the more will be in focus.
I've realized I've talked a lot about what is in focus, what is not, what tools to use to get what you want in focus, but I haven't yet talked about focus and what it is. So lets touch on that now. Focus refers to the sharpness and clearness of an image. When I say something is "out of focus" what I'm really saying is that its blurry, and when it is "in focus" the lines are sharp and crisp and clear. On the lens of your DSLR you will notice a little A | M with a switch. That switch is to go between auto focus and manual focus. Mess around with it on manual to get your desired look.
Our eyes can adjust to tell what is the color white, our camera though are not so sophisticated. Coming back to that issue of light, light can change what we perceive as white to be yellow-y orange or blue-ish. Light is often referred to as either "hot" or "cool" and I bet you guessed it, when light is hot it turns whites yellow-y and when its cool it comes off as blue-ish. With out getting too complicated you can actually go into your setting on manual and under "shooting menu" you can set the white balance for the kind of light you are shooting in. everything from florescent lighting to cloudy day light, your pictures will never have a weird color tinge to them again!