Whatever the reason you bought your DSLR was, at some point if you are anything like me you will ask "why do these different present modes take different types of picture?" well the answer is simple aperture, shutter speed and ISO.
As long as time permits most photographers only use one setting on their DSLR and that is Manual, by controlling the aperture, shutter speed and ISO level you achieve anything. This article is design to help you understand what aperture is and how it affects the photographs you take.
The aperture or F number is basically the size of the opening through which the picture is taken, confusingly the lower the number the bigger then opening! If you look at the picture next to this article you will see examples of this.
Why change the aperture? The aperture effects the photo in a number of ways, firstly it effects the amount of light taken in so the larger the opening the more light is allowed in. Secondly the size of the aperture affects the depth of field in the shot, the smaller the aperture the larger the depth of field will be.