Then switch to knit one purl one for five rows. Continue in in knit one purl one pattern for five rows bind off. For the rest of us cast on three stitches and knit. Next row make one stitch purl row make one stitch. Continue increases every other row until the gusset is as wide as your crotch.
People vary so measure and check.
When you reach your crotch width begin to decrease every other until only three stiches remain. Find gusset center and pin to leg seam top. Sew to side piece cantered. Take other side peice and join keeping gusset centered on second side. Crochet belt or make I-Cord and thread through holes in waist band.