To mix and apply fiberglass resin, first, make sure to wear protective gloves, goggles, and a respirator mask. Start by measuring the required amount of resin and hardener according to the instructions provided. Mix the resin and hardener together in a clean mixing container, ensuring thorough blending. Stir the mixture slowly and steadily to avoid creating air bubbles. Once mixed, apply the resin using a brush or roller onto the fiberglass surface, working in small sections at a time. Ensure even coverage and smooth out any excess resin. Allow the resin to cure as per the manufacturer's instructions before handling or sanding.