Finings is the generic name given to clearing agents used in beer or winemaking. The principle behind all forms of finings is to act as a flocculent, which causes impurities to gather through the medium of positive and negative charges into large enough clumps to make them sufficiently heavy for gravity to take effect and allow them to sink to the bottom of the fermenter.
Finings are normally added 2 days before fermentation is complete. However, I do not like to open my fermenter and expose it to air so I recommend you add the finings at the beginning.
How to use finings:
Dissolve the finings in a cup of warm water (not hot) and add to the wort approx 2 days before kegging/bottling your beer. Due to the added risk of infection by opening the fermenter at such a late stage in fermentation, some brewers prefer to dissolve the finings in a cup of warm water (not hot) and add to the wort at the preparation stage, just before pitching the yeast.