Yeast is added to the cooled wort in the Fermentation Vessel.
The yeast converts the sugars that were produced by the malted barley, producing Co2 & alcohol.
This process takes 3 to 10 days, depending on the strength of the beer you are fermenting. A barley wine will take longer to ferment than a beer of say 3.5% ABV. We use wet yeast which is re-pitched from brew to brew for several generations.