I have a D90. Its my first DSLR, but I might say that i have played with it quite a bit. To understand DSLR you need to know the concept of exposure:
- Exposure ...in layman's terms...how bright a picture appears or how clear it is.....is determined by:
= Aperture
= Shutter speed
= ISO
For the lens to project an image on the sensor inside the camera body, the limiting factor is the size of the HOLE that lets in lgiht through the lens. This is represented by F#. They are a bit reverse in their numbering as it represents a fraction, but the order being F2 (bigger aperture) -> F32 (smaller aperture). More light = more exposure...implies Bigger aperture (smaller F number) means you can get a lot more light in through the lens. However, lenses with bigger apertures are expensive and are called FAST lenses. Used for sports etc.
Next, shutter speed...determines how quickly the camera opens and closes the shutter. This is pretty simple. If you keep the shutter open too long, you will get a lot of light in the sensor. Shown as 1/100 of a second, 1/200....1/800...1/1600) means faster shutter speed but u can imagine...less time the shutter is open= less light incoming = less exposure.
So shutter speed and aperture go hand in hand. one goes up, the other has to come down. Its about balance. For instance,, if u want to take things with light trails...i.e, some of those artsy waterfall pics where water looks like a continuous line....the trick is to lower shutter speed...ie., shutter speed is 1 or 2 seconds. So shutter will be open for soo long and anything moving will be recoreded as a motion blur. On the other hand for sports, u want a fast shutter speed to freeze the action...so increase shutter speed...I would go around 1/600 depending on the type of sport. But keep note...since your shutter speed is low...your picture will be dark. This is as I said...lesser light coming in....hence...balance it my increasing aperture...bump up aperture to F2.8 (if u got such a lens). That will balance it.
Lastly...sometimes...u cannot get correct exposure with this...so another thing can help...ISO. Iso is sensor sensitivity to take in light pixels. If you increase ISO...you are increasing the sensitivity...so that means you can take pictures in some dark places. However, as sensitivity goes up, image NOISE goes up. So I wouldn't go above ISO 800.
Lastly...there is a factor called depth of field. IMO that is my most important one. You must have seen those amazing macro shots that PYGO posts on this forum. Notice how blurry his backgrounds are? that is depth of field. For PRIME lenses (lenses that are expensive and fixed focal length, they have LOW F#...like my macro lens is F2.8) it means that this lens can increase the hole through which light reaches the sensor to a very big size. When a lot of light is coming in....i.e., HIGH aperture = SHALLOW DEPTH OF FIELD...i.e., the plane of focus is very shallow...so..you can focus on the single pitcher tooth on a N. bicalcarata for instance...while everything else is out of focus...looking blurry.
For sports shots, if you are looking for a lens...let me recommend the 24mm or 50mm F2 nikkor lens. Its a <200$ lens that is amazing for the money. Very fast. It is NOT a macro lens, but an amazing potrait lens...which will give some stellar images.
There...thats ur crash course.