Saccharomyces cerevisiae, also known as brewer's or baker's yeast, doesn't commonly grow on grape skins in the vineyard—in part because it can't tolerate direct sunlight well—but it's the species most essential to winemaking, and it fiercely defends that role.
Yeast is essential to the winemaking process: It converts the sugar in grapes to alcohol during fermentation. Yeast is added to most wines—winemakers will inoculate with a strain of commercial yeast (as opposed to native yeast) that is efficient or emphasizes flavors or aromas they desire.
The most common yeast generally associated with winemaking is Saccharomyces cerevisiae which is also used in bread making and brewing.
Nitrogen also helps the yeast to produce higher levels of natural enzymes, which means your wine will clear and age quicker. Having plenty of nitrogen will also increase the yeast's tolerance to alcohol. The most common source of nitrogen is Yeast Nutrient it comes either in powder or tablet form.