lots of places on the web with directions, including here. I believe Eva has that in the archives somewhere. anyways, it's realllly easy. bring your last stitch (in the first color) up to the last yarn-over before you would complete the stitch. put the next color on your hook and draw it through to complete the stitch. for instance, if you are doing dc, after you've yo'd and pulled through the stitch, yo and pull through ONE time, then tie on the new color, and complete the dc. which ever stitch you are using, bring it to the last yo, and switch colors. when you come back and want to change again to the old color, do the same thing, but instead of tying on the new color, its already there, just bring it up from the front, and drop the present color to the back. here's a link:
http://vickisdesigns.tripod.com/graphs.htm