Topstitch

The Topstitch is a means of reinforcing a seam's structure by stitching through all the layers of fabric that make up the seam. Topstitching is used all the time to "neaten-up" a seam and create a more visible structural line, and it's also used when finishing bias tape along a sleeve or other opening.

Unless otherwise indicated in a pattern, a topstitch is a normal-length (2-3) straight stitch across all layers of fabric that is fixed at both ends. Because a topstitch will be visible on the final garment, it's important the stitch be as straight and even as possible, and is often as close to the seam edge as possible.

Practice...
To practice a topstitch, simply use leftovers from practicing your Simple Seam. Fold along the seamline and then stitch along the top. As you practice, try to get as close to the edge of the fabric as you can while still maintaining a straight line. If you can get it between ¼" or even ⅛", that would be ideal.