|The three-step (or multi-step) zig-zag is a stitch found on most machines. The symbol looks like a zig-zag where each zig and zag is made up of three short dashes (stitches). One way to use this stitch is to make bar tacks, for example to secure pocket or fly openings, or to attach belt loops.
To make a bar tack, simply disengage the feed dogs so that the fabric is not fed forward (I suppose you could also set the stitch length to 0). In most cases, you'll want the widest possible stitch on your machine, but try a few widths to see which you like best. Then just place the fabric under the needle, lower the presser foot (not a straight-stitch foot, mind you!) and let the needle sew back and forth a few times. Remember that the bar tack will form left-to-right.