Malted barley is the most common brewing grain but rye, wheat and oats are also frequently used. from the grain we get colour, sweetness and it also contributes to the body of the beer.
Hops are usually dried in an oast house before they are used in the brewing process. undried or "wet" hops are sometimes (since ca.1990) used. The wort (sugar-rich liquid produced from malt) is boiled with hops before it is cooled down and yeast is added to start fermentation.
This isn't simply something that comes from a tap or a well. really its all about the specific composition of the water - whether its soft, hard or high or low in calcium, sulfites,magnesium and other minerals.
Yeast are single-celled micro-organisms that reproduce by budding. they are biologically classified as fungi and are responsible for converting fermentable sugars into alcohol and other byproducts. there are literally hundreds of varieties and strains of yeast. in the past, there were two types of beer yeast: ale yeast.(the "top-fermenting" type, sacchoromyces cerevisiae) and lager yeast ("the bottom-fermenting" type, sacchoromyces uvarum, formaly known as sacchoromyces carlsgerggenis).