Shutter:


All cameras works the same way. Each one of them is simply a box, a hole and a light-sensitive sensor (or film when using filmcameras). The hole lets the light into the box. When the light enters the box and strikes the sensor and a photo has been taken.
The shutter controls the length of time the hole stays open for. The final exposure of the photo will depend upon this. Let us say the "hole" is kept open for just 1/1000 of a second, during that short length of time not much effect is made on the light sensor and film. Compare this with keeping it open for a second.

The shutterspeed is important for action photography, if you want your subject to be still on the photo, you have to use a fast shutterspeed (ex.1/1000) but if you want to show some movement in your picture you should go slower.
Normally your camera won't let you choose a shutterspeed longer than 30 seconds, if this is what you need, you have to choose option B (short for BULB) which will let you keep it open for as long as you need.
When taking photos in dark conditions a tripod with a camera releaser will help to avoid unwanted shakes.

Here is a video to help all of you visual learners see for yourself exactly how the shudder button works:



Aperture:

Aperture relates to the size of the hole that opens when the camera is taking a photo. The larger the hole, the more light is taken in i.e. the brighter the photo. When we are talking about aperture we talk in f- numbers. The sequence of full f-stops runs as: 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, 45, 64. But where the number range starts and ends all depends on the lens you've got. It might seem confusing that the larger the hole the smaller the number. A good tip to remember is to think about it as pieces; let's say there are two cakes, the first cake is to be cut into 2 pieces and the other one into 45, which cake would you like to take your piece from?
The aperture won't just have an effect on the exposure, but also on the depth of field in a photo.

Shutter and Aperture Used Together:


Before you take a photo you always have to ask yourself what you would like the photo to look like. Do you want to be able to see each individual car on the motorway clearly? Then you have to focus on keeping the shutterspeed fast, and in return the aperture might need to be bigger and you will have to sacrifice some depth of field. To be able to work faster in these situations you can go with the option "Tv" (Shutter Priority) on your camera, this lets you choose only the shutter and the camera will it self figure out which aperture to use for best exposure result.

An opposite example of the above could be when you are taking a photo of a friend and you would like to have both your friend in focus and the object in the distance, then you will need a small apperture, increasing the depth of field but by doing this you will need to go for a slower shutterspeed.

This can lead to camerashake which you can solve by using a tripod and by telling your friend to not move around too much. If you already decided which aperture you want to use you will save time and energy choosing the "Av" (aperture Priority) on your camera this means that you dont have to keep on changing the shutterspeed all the time when the light is changing.