Make it like you would a pillow case. Lining and your fabric right sides together. Sew up 3 sides. Turn inside out. Fold over a 1/4 inch hem on fourth side and sew. Place your straps on the outside, pin and Sew them to fabric. Fold bag in half, sew right sides together. Turn right side out. If you want to add pockets do that before you sew it together.