Use the stitch length to control how tightly together the zigzags are.
Use the stitch width to control the width of the zigzag line.
The needle stitches into the fabric:

and close to the edge:

Use the stitch length to control how tightly together the zigzags are.
Use the stitch width to control the width of the zigzag line.
The needle stitches into the fabric:
and close to the edge: