The first part is to clean the whole parts of the mold really well from any dust or grime build up. This will help in creating a perfect duplicate with no hitches. Use a rag and acetone for this purpose and clean all parts.
Now apply a mold releasing agent to the mold. This agent will help in taking out the fiberglass from the mold easily like you grease pans for making cakes. Apply the agent to the surface of the mold.
Now use a sharp razor to cut the fiberglass mats that you have in shape of the mold. The cut mats should be able to fit in the mold without any difficulty. You need a sticking gel to hold the mat to the mold. Use the small bucket to mix the gel coat and the hardener together by constantly stirring. Now coat the surface of the mold with this mixture using a roller. Allow the gel to harden on the mold.
Take another small bucket and mix in the fiberglass resin with the hardener. Stir these two well. Use a roller to apply this mixture to the surface of the mold. Place the first mat on the mold surface. Apply a layer of resin on the mat and then press on another mat. Repeat until all the mats are applied and the mold is full. Let the mold rest until the fiberglass is set and cool.