Hi,
My advice would be to start in Av mode. (Turn mode dial to Av) This will automatically set the exposure for you, but let you control the amount of 'stuff' that is in focus. Below are a few hints, it is a long read, but play with one thing at a time and it should all make sense.
1. Focus
The camera has automatic focus, but has 9 focus points. To avoid any confusion I would start by setting the camera to use the centre one only.
Press the button that looks like a plus sign in a square box [+]. (located top right) Look through the viewfinder and rotate the wheel (next to the shutter button) until just the middle red LED lights up. Then press the [+] button again.
When you take a picture, you need to focus the camera first. Point the middle square box in the viewfinder at what you want to focus on and half press the shutter. Note it's important to point it at something that has good contrast (eg detailed - Not a plain white wall or sky!!) The camera should beep, and a green light in the lower right will remain lit. This tells you the camera has focussed the shot.
Without releasing the half pressed shutter. Re-position the camera to compose the shot and then fully depress the shutter to take the photo.
2. Shutter speed
This needs to be set about 2x your lens focal length (or higher) , to prevent hand shake from blurring the image. For example at 50mm you need 1/100 of a second or higher - at 18mm it needs to be about 1/30 or higher.
If you use image stabilisation (IS) you can shoot with slower speeds (about 4x slower). Eg 1/100 could be 1/25.
HOWEVER - depending on the subject, slow shutter speeds also lead to 'subject' movement. For example shooting a person standing still use 1/60 or greater. For kids jumping about I would use 1/250 or greater. For a jet shooting across the frame I would use 1/1000 or maybe even 1/4000!
In Av mode, look through the viewfinder half press the shutter and spin the wheel, you will see numbers like 160, 200, 250, 320, 400, 500 etc. This is the shutter speed.
3. Aperture
This controls the 'Depth of Field' or the amount of the image that is in focus. When you focus the camera (by half pressing the shutter button), the camera will focus on one point (or a better description is at a particular distance). Objects at increasing or decreasing distances from that point become progressively more out of focus. (or blurred)
Objects located at a similar distance to the focal point are said to be within the depth of field or 'in focus'. Exactly how much the image needs to be in focus, depends on the size you print the image and how closely the print is examined.
You control the depth of field by adjusting the aperture of the lens. In Av mode spinning the wheel adjusts this. Look through the viewfinder, half press the shutter and spin the wheel - you will see numbers like 3.5, 4, 5.6, 8, 11 etc... This is the Aperture ratio. (people typically refer to it as f3.5, f4 etc...)
Big numbers like 8, 11, 16 mean lots of depth of field. (more in focus)
Small numbers like 2.8, 3.5, 4 means little depth of field (less in focus)
Be careful with f16, f22 and bigger values as the whole image will start to blur due to a problem known as diffraction.
Experimentation is the key here, take a picture at as many apertures that you can and look at the results, you will soon learn what typical values you need.
Also Note that :-
1. The focal length of the lens also affects the results. (Long focal lengths = little in focus)
2. The greater the distance to the subject, the easier it is to also get the background in focus.
Again experimentation is the key. Change ONE parameter at a time, take a shot and note the results. Keep an eye on the shutter speed when you do this. If it gets too slow, it will mess up the shot.
4. ISO
This sets how sensitive the camera is to light. (by pressing the ISO button and spinning the wheel, then re-press ISO button to set it)
When the shutter speed is too slow, it's necessary the raise the ISO. The penalty is that the higher the ISO, the more noise there is in the image. So sometimes using Flash or a tripod is a better option.
This is just a brief introduction - Have a really good read of the manual - and play with the camera while doing this.
However most importantly - have fun with the camera and don't get too stressed when things go wrong. A DSLR is a learning experience that takes time, but the beauty of digital is that (unlike film), the failed shots don't cost anything!
Hope this helps
Regards
Andy