Here are a few sites that will give you the idea.
http://www.onlinearchery.org.uk/advice/tune/string_making.html
http://tradgang.com/endless/ejig.html
http://www.ohiosportsman.com/forum/showthread.php?t=34557
http://daohead.com/loose-stuff.html
The jig I have here is different from all of these, and is close to 50 years old. I probably only have it because the jig is so easy to build that I’ve not carried this one as I traveled the world; I just made new ones to use, wherever I was.
I think you can get the idea from these but if you need more help I can take photos on mine to post. The all-wood jig in the first site listed is closest to mine in construction, but not exactly the same.
Ed