Many people are working with table saws that maybe are missing pieces or missing accessories. A table saw fence is one of those things that can land on your “I need one of those” lists. You don’t need to always buy this particular piece though, you can just as easily make one.
Woodgears.ca has a great overview on how to make your own table saw fence. It’s not really that complicated, but you need to make sure everything is squared up properly and that the fence can be clamped easily and securely.