Built-in stretch stitch (c). Differing from brand to brand, these stitches are designed to incorporate stretch, so that you do not need to stretch the fabric as you sew. Some stitch styles, like the bottom two samples, are a pattern of zigzag and straight stitches that stitch and finish the seam in one pass. Check your manual for stitch settings.
TIP The cut edges of knit fabrics do not ravel, but they often curl. To minimize this problem, the seam allowances are usually finished together and pressed to one side.