The following video from Alpinord of Slidewright Tools provides visual aids and another perspective on diamonds, files and edge tuning. There are a couple more bonus videos for learning how to hot wax and brush and scrape afterwards. Be sure to check out his website for more tips or give a shout if you have questions.
Edge Tuning-So Easy even an Adult Can Do It
Side walls need to be modified to remove the portion at the top of the edge so a diamond or stone is not obstructed from cutting or polishing the edges. Here is a video from SVST using a side wall planer: