The easiest way would be to slowly pour liquid chlorine around the perimeter of the pool while someone follows behind you with a pool brush attached to the pool pole and brushes the fiberglass from the wall down and across the bottom of the pool. This will protect from having chlorine settle on the bottom of the pool and it will disburse the chlorine throughout the water.
You can do this with chlorine granules like Cal-hypo also but you need to be sure that the granules are complete dissolved in a bucket of water before you pour into the pool. Otherwise you run the risk of chlorine granules settling on the fiberglass and bleaching it.
Just be sure to thoroughly brush the walls and bottom of the pool (especially if you use granular chlorine).