Cut the elastic the circumference of the waist minus approximately 4 inches (10cm). Sew together into a circle, using a zigzag stitch.
Quarter the elastic, using straight pins to mark the back seam, the opposite side, and then match them up and pin the other two quarters of the elastic.
Use the same technique to mark the quarters on the boxer waist part.
With the boxers turned inside out, apply the elastic to the outside of the waist area, with the right side of the elastic facing out.
Pin at the previously marked quarter sections on both the boxer fabric and the elastic.
This is what it should look like with the elastic pinned, right side out, to the boxers, right side in.
Make sure to check that your elastic is far enough down from the top of the boxer fabric that you can sew it to the fabric without catching in the edge of the elastic. This will make turning the elastic to the outside easier and look more professional.
On my machine, stitch number 6 is the lighning zigzag stitch. This is much similar to the zigzag stitch, except the stitches are broken into sections to allow for greater stretching. It is purported to be more sturdy when sewing elastic for waistbands and other applications requiring the elastic to have more give.
This is how my machine looks on the lightning zigzag stitch setting. Since it's an automatic and computerized machine (to an extent), it chooses and adjusts the settings again.
(Continued on next entry due to photo limitations)