The tradition of wearing kilt pins comes from Queen Victoria. She allegedly used her hat pin to secure her kilted skirt on a windy day, protecting her modesty and starting a tradition.
The addition of a kilt pin to a kilt is purely an aesthetic choice. If you do wish to wear a kilt pin, it should be placed on the right of the kilt, through the front apron (this will prevent tearing), about 4 inches from the bottom of the kilt and 2 inches from the fringe.
We have a giant collection of kilt pins, from the basic kilt and skirt pin to the chrome finished Thistle Crown Chrome.