This section is from the book "School Needlework. A Course of Study in Sewing designed for use in Schools", by Olive C. Hapgood. Also available from Amazon: School Needlework: A Course Of Study In Sewing Designed For Use In Schools.
A gusset is an angular piece of cloth, inserted in a garment, to strengthen and enlarge an opening.
1. Find the middle of the side of the cloth not hemmed, and cut two inches and a half, by a thread.
2. Make a hem on each side, having it one-eighth of an inch wide at the top, and turned to a point at the bottom.
3. Find the middle of the rounded side of the gusset, and crease to the opposite corner.
4. Baste with even stitches along the crease.
5. On all the sides, fold and crease one-fourth of an inch.
6. Cut off all unnecessary thicknesses of cloth in the folds, and baste the folds down.
7. On each side, five-eighths of an inch from point a (Fig. 50), make a pin-hole; then fold and crease from pinhole to pin-hole (Fig. 50, b to b).