Pitching yeast is the brewing term for adding yeast to the unfermented wort. If the wort, now in your fermenter, is approximately room temperature you can pitch the yeast. If the sides of the fermenter are warm to the touch then let the wort cool to room temperature before pitching the yeast. Note: A package of brewers yeast typically contains an amount for a 5 gallon batch so pour approximately half a package into the fermenter. A little more than half is fine and it's probably better to be a little over than a little under.