When brewing with hops, it's best to place them in a sanitized muslin hop sack to minimize hop particles in your finished beer. Tie off the open end of the sack, and place it in your boiling water just before removing the heat.

Proceed as usual, leaving your hop sack in the fermenter for the entire fermentation, unless your recipe directs you otherwise. Just throw it away after bottling your beer -- it's not reusable.