This page contains links to all relevant documents for Assignment 5.
Here is a very useful Emacs Prolog mode and here are instructions for setting it up, which are basically the lines you have to add to your .emacs file in your home folder. It sets ".pl" to be the default extension for Prolog file, which is what SWI uses.
Of course, you can also use other editors than Emacs, but if you decide to use it, this Prolog mode can be very useful as it already does some syntax checking for you. This way it can save you a lot of time when e.g. looking for the missing ',' in your code.