This instructable will explain how to use the main features of a Digital Single Lens Reflex (DSLR) camera in manual mode.
I assume you know your way around the camera roughly, like where the mode dial is and other buttons and dials.

Step 1: Manual Mode

First put your camera into Manual Mode by turning the main mode dial (if you have one), if you don't it should be in the menu somewhere.

Step 2: Shutter Speed

Shutter speed is how long the image sensor is exposed to light coming through the lens, so, longer the shutter speed, the more time the sensor has to record the light, the brighter the image and vice versa. Shutter speeds range from seconds (for really dark environments) to high thousandths of a second (for really bright environments). A long exposure can be used creatively to get a blurred image or a short exposure for completely frozen motion.
Idea credit for the light dome goes to: Dark Light
His Instructable on how to build a tool for making the light dome is HERE

Step 3: Aperture

The aperture is a hole in the lens that you can adjust the size of to allow more or less light to flow through. The aperture is also used for changing the depth of field and the brightness of the picture. The F-number is the value you alter to control the size of the aperture. Unlike what you might expect, the higher the F-number the smaller the hole in the aperture and deeper depth of field.
Most lenses nowadays don't have a aperture adjustment ring on the lens, there's usually a dial on the camera body that you can adjust it with. I like to use a low F-number for a shallow depth of field so objects in the background don't stand out as much as the object your trying to take a picture of.

Step 4: ISO

The ISO sensitivity is how sensitive the image sensor is to light. Inside I tend to use around 800-3200 (anywhere above that and the image comes out looking too noisy or grainy) and outside I use between 100-800. Now, you could use noise as a creative aspect of your photograph but if you are, only a little bit as it can get pretty harsh and overpower your pic.

Step 5: Shutter Speed, Aperture, ISO

So, you now know that the shutter speed, the aperture and the ISO sensitivity work in conjunction with each other to effect the exposure of the picture, but also have side effects of their own (blurred or frozen motion, depth of field and noise).

Step 6: Happy Photographing!

This is my first Instructable and I hope you got something useful out of it, and if you didn't, I hope you enjoyed the pictures.
You'll soon find that using a DSLR is a lot easier to get better pictures from that a regular compact camera. Also don't be afraid to be creative and if you have photos you would like to post in the comments, by all means do that!