Shutter speed function is a mode whereby the exposure timing is controlled by you, other than that ISO/Aperture is controlled by the camera's metering.
If you want to freeze action, use a high shutter speed, if you want to make action into a blur, use a lower shutter speed. Note that you can only handhold safely for different focal lengths with the rough formula (1/focal length), if you have correct technique, maybe 1 or 2 stops more.
If you are not catching any ball about what I have written here, best to pick up some books on the basics of photography, and start reading up first.
If you are new to photography, then perhaps the best way to start is either to enter the woods right away with manual photography, that's what I did; or to start with program mode.