Learning to use your DSLR

Shutter Speed : This is how long your exposures are. You'll see a meter on top of your camera and in the eyepiece with a marker in the middle. This marker is what the camera thinks the correct exposure is. In AUTO mode the camera will automatically do this for you but in MANUAL and AV mode you'll have full control over it. Think of it like driving a car. The speed limit is 30 so using the pedals on the car you control the speed. So with a camera you're just using the wheel to make sure your exposure is also at the correct speed.
If your mark is too far to the left your image will be under-exposed and what this means is your image will appear darker than it should be the cause being that not enough light is being allowed into the camera's eye. And if your mark is too far to the right then your image will be over-exposed and what this means is that your image will appear lighter than it should be the cause being that too much light is being allowed into the camera's eye, flooding the image. Under and over-exposed images can be used to good effect when you know how to use them properly. But when the mark is too far to the left or too far to the right you're going to get images which are either too dark to see or too flooded with light to use.

F number : The F number is the camera's way of isolating a subject. Just like your eyes can isolate a subject. An example of how the F number works is to hold your index finger in front of your nose at arms length. Focus on the tip of your finger. Notice how everything in the background is still in focus ? Okay.. now slowly move your finger towards yours nose focusing on your fingertip the entire time Notice how the closer your fingertip gets to your nose the more the background melts away until your attention is on your fingertip and the background becomes all blurred out ?

That's pretty much what the purpose of the F number on your camera is. Subject isolation
The lower your F number is, the more out of focus your background is going to be but this has a few rules.

1. The further away from a background your subject is, the more apparent the effect of the F number will be. So if you're shooting F2.8 and your subject is laying flat against a wall, you're not going to get much image isolation at all. However if your subject stands 4 - 5 meters away from the wall then the difference is going to be huge and the background will melt away into nothing. This is also defined by the focal length and distance you are from your subject.

The effect of F2.8 on a 70-200mm lens will be much more evident if you're standing far away and zoomed to 200mm than if you use 70mm zoom of the same lens at F2.8 so the longer the zoom, the more evident the effect becomes. I've found that F5.6 background blur on my 400mm is just as effective as F2.8 on my 70-200mm lens due simply to the extra focal length. A lower F number will also vastly increase your shutter speed where as a higher F number will make your shutter speed a lot lower. The background blur effect is more commonly known in photography as Bokeh

2. But what if I dont want my background out of focus ?? There's something I want in the background as well as my subject ! Just as a lower F number gives you subject isolation, a higher F number does the opposite. So if you want your background to be in focus along with subjects in the foreground you'll need to crank up your F number. Just remember as noted in rule #1 you'll get a much lower shutter speed at higher F numbers which can be compensated by taking photo's on a bright sunny day, using a flash unit or increasing your ISO

3. Be careful when shooting close up at low F numbers !! At F1.8 if you shoot a close up portrait of a persons fact then dont get TOO close. If you do then you risk having eyes in focus but an out of focus nose, ears ( and if the face isnt head on you'll also get photo's where 1 eye is in focus and the other one is not !! ) This is due to the extremely narrow DOF ( depth of field ) of a F1.8 apeture. To avoid this you can either take a step back and then crop the image or increase your F number.

ISO : ISO is the camera's way of creating artificial light. It's a brilliant concept and often very well done - espcially in the higher end of the DSLR market. When you look at your AUTO mode EXIF data you'll see " ISO " and it'll have a number next to it. The lower the number is, the more light you had available at the time of the shot. When you're shooting, I find on lower end zooms ( 200mm and below ) you're going to be looking at 1/250th handheld for static subjects and 1/640th for moving ones. When you are unable to get these speeds, instead of risking getting blurred photo's simply increase your ISO and you'll get the extra light ( and shutter speeds ) you'll need. The only downside to cranking up your ISO is in certain situations you'll get noisier images but since this is 2010 ISO noise levels on most DSLR's now are perfectly acceptable compared to a few years back when you'd get high noise levels at ISO 800 and 1600 was a last resort because it's noise levels rendered most images unusable. On a bright sunny day you'll seldom if ever need to go above ISO 200 even at higher F numbers. And in situations when it's dark and you dont want noisy images you can keep your ISO low and use a flash.

White balance : The WB setting on your camera can work in 3 ways. You can use the ( often very accurate ) white balance settings appropriate for your shooting conditions : Sunny, Cloudy, Flash, Tungsten et all.. or you can use " AUTO WB " which personally I wouldnt recommend as the previous options give much better accuracy. You can also set your own K temperature. White balance is the camera's way of getting the colours you see captured as accurately as possible. When you're setting your own K temperatures, I recommend you look at this to get a rough idea of what to expect.