Viewfinder
First, when we look through the viewfinder, we are actually looking through the lens (via a highly-polished mirror). This is a big advantage over Point and Shoot (P&S) cameras, as you are seeing exactly what will end up in your final photo.
Taking a Photo
When we press the shutter button, the mirror flips up and out of the way. The lens stops down to the correct aperture, and the light goes through the lens and hits the digital sensor. The amount of time the shutter stays open is called shutter speed, and this value, along with the aperture setting, determine the exposure of the photo. Aperture is simply how big of an opening there is in the lens. The combination of aperture and shutter speed can drastically change how a photo looks, and it is this combination that P&S cameras (and DSLRs on auto modes) perform automatically. With a DSLR, you have full control over all settings, and therefore much more control over your photos.
The Sensor
Just like all digital cameras, DSLRs have digital sensors that record the image. These, like film, are sensitive to light. The sensor converts light to electric signals. Each sensor is made up of millions of pixels. The larger the sensor, the more pixels, and the better quality the image will be. More pixels also means larger prints can be made from the files.
The Processor
The data captured by the sensor is processed by the cameras processor. This is just like a processor in a computer. In a DSLR, this processor applies filters, calculates correct exposure, performs red-eye reduction, and most importantly it compresses the image in the correct format – usually JPEG, and sometimes RAW. This file is then saved to the memory card.
Camera Modes
Almost all digital cameras have dials which allow you to use different mode settings. Each of these modes take over certain controls of your camera to optimize your photos for the given mode. Some cameras have modes for Fireworks, Bright Snow, Portraits, Landscapes, and so forth. Most of these are self-explanatory, but it is important to understand the modes of your camera – it is a key step in mastering the controls and taking your photos to the next level.
Info – Camera Modes 
http://digital-photography-school.com/digital-camera-modes
Rebel XT Lessons
http://usa.canon.com/content/rebelxt_tutorial/rebelxtlessons.htm
Understanding Digital Camera Sensors
http://www.cambridgeincolour.com/tutorials/camera-sensors.htm
Care and Handling
Digital cameras are fragile pieces of equipment. Digital SLRs are much more solidly built than Point & Shoot camera, but they still require careful use and proper handling. The most obvious piece of equipment that needs to be treated with respect is the lens, which protrudes from the body. The front of the lens should be covered with a UV filter so that if anything touches it and scratches it, the actual lens element is not being affected. Keep your lens cap handy, and use it whenever you are not taking photos. Keep the body of the camera clean, and keep it in its case when not taking photos. Be careful when cleaning the lens and LCD screen – only use a soft cloth to prevent scratching.
How to Hold the Camera
Info – Holding a Camera
http://digital-photography-school.com/how-to-hold-a-digital-camera