Shutter speed determines how long the shutter will stay open for, this is the camera's ability to freeze motion. The longer that the shutter stays open for, the more motion that is picked up in the image.

Setting the correct shutter speed on your camera can go a long way to getting sharp images. As a general guide for hand holding your camera try and aim for a shutter speed that is equal to or shorter than 1/focal length of your lens. For instance if you have a 100mm lens then a good shutter speed would be 1/100 sec. Below is an example of camera shake at a slow shutter speed.

There are a lot of different ways to change your shutter speed without affecting your exposure, here are some to try:

For increasing your shutter speed (when you want to freeze motion).
High ISO eg. 3200.
Wide Aperture eg. F/2.8.
Bright lights eg. Sunlight or flash lights, you can also try a torch if it's really dark.

For decreasing shutter speed (when you want to capture motion).
Decrease ISO eg. 50.
Small aperture eg. F/22.
Neutral Density filter.
Polarizer filter- plus has the added bonus of being a polarizer.
Shade the subject with an umberella etc.
Cloudy sky as opposed to full sun.
Early morning or late afternoon when it's a little darker and the sun is not high in the sky.