There are 8 snaps to apply. For best results, try playsuit on and safety pin straps and sides to fit your baby. Mark new snap placement with holes made by an awl or with a pen. If baby is not available, use the snap placement dots marked on the pattern, but trying on garment will give you a better fit.
Try hammer-on metal snaps like Birch Poppa Fasteners. They come in kit form with an applicator stick and instructions on the pack and are much faster to apply that sew-on snaps. An even easier option that I've fallen in love with are plastic snaps (see next pic.)