Much of this information is from Wikipedia only in condensed form. Obviously, there is a lot more involved but here’s a simple reference guide:

HISTORY– Brewing has taken place since around the 6th millennium BC, and archeological evidence suggests that this technique was used in ancient Egypt. Descriptions of various beer recipes can be found in Sumerian writings, some of the oldest known writing of any sort.

BREWING – the production of beer through steeping a starch source (commonly cereal grains) in water and then fermenting with yeast. The basic ingredients of beer are water; a starch source, such as malted barley, which is able to be fermented (converted into alcohol); a brewer’s yeast to produce the fermentation; and a flavoring such as hops which aids in preservation. Fermentation may take place in open or closed vessels. There may be a secondary fermentation which can take place in the brewery, in the cask or in the bottle. 

 >>>> So, water + barley + temp = MASH.  Boiling seperates the liquids from solids = WORT.  The wort is boiled to remove any germs.  Add spices for flavor.  Yeast and oxygen added for fermentation process yielding the alcohol (ABV).  Yay!

WATER – Hard water is better for stout.; soft water for pale lager; gypsum in the water for pale ales. (I did not know this! Who knew the makes a difference?)

MALT – Most common starch source; grain is soaked in water then partially dried in a kiln which produces enzymes converting the starch to fermented sugars (the alcohol!). Different roasting times and temperatures produce different colors of malt from the same grain.
(Malt is what gives sweetness to the beer. The darker the malt, the darker the beer.)

HOPS – Hops contribute floral, citrus, herbal aromas and flavors to beer as well as a bitterness that balances the sweetness of the malt. Aids in “head retention”, the length of time that a foamy head created by carbonation will last. The acidity is a preservative.
(The higher the hops, the more bitter the beer will taste).