How to make a simple zig zag stitch??
I would recommend picking up the book "Sailmakers Apprentice". It covers all aspects of sails, from design, material selection, construction, maintenance, and repair. It is one of the best books on the subject I have found. If you can''t find a copy on the shelf, you can order it at either a Boarders or Barnes & Noble.
You will find a nice section in there on the various stiching techiques used in sailmaking, and their uses. Clearly written and an excellent guide for the layperson. I highly recomend it for the "Self Sufficient" sailors among us.