Assess the damage and remove loose or broken off shards of the fiberglass by cutting them away with a knife or jigsaw, so you are left with a smooth, nearly geometric hole in the fiberglass.
Sand the area around the hole and bevel the edges with sandpaper or a grinder, if the damage encompasses a large area. The entire edge of the hole should be beveled to accept the fiberglass patch repair.
Cut strips of fiberglass to fit over the hole by laying them on the hole and trimming away excess, leaving an inch or two of overlap onto the fiberglass. If the hole is very large and the fiberglass sheets drop into the hole, cut a sheet of laminate slightly larger than the hole and apply PVA (polyvinyl alcohol) to the surface facing your repair. Attach it underneath the repair area with strong duct tape.
Lay the fiberglass sheets over the repair area. Mix the resin with the hardener in your fiberglass repair kit, and apply the fiberglass resin to the sheet. Spread the resin over the entire sheet in generous amounts so the entire area, including the overlap is covered in resin. Let this dry for several hours or until the entire surface is solid.
Sand the repair to make it flush with the rest of the fiberglass, using 200-grit sandpaper. For large areas use an orbital sander and pad. Add primer to the repair area and let it dry. Add a top coat to finish the repair.