Beer is an alcoholic beverage produced by a complex process, known as brewing. First step: hot water is mixed with crushed malt, producing saccharification of starch and fermentation of the resulting sugar. This mixture is usually flavored with hop or different herb or fruit. Some yeast is added, to start the fermentation process, creating alcohol and carbon dioxide. Different ingredients and working techniques change the resulting beer type.
Beer is among the world’s oldest alcoholic beverages: we have written recordings in ancient Egypt, but the earliest known evidence dates back to about 3500–3100 BC. Ancient Greek and Romans used to prefer wine, but did not disdain beer during banquets in honour of the goddes Demeter (Ceres for Romans). In Europe, Beer was spread by Germanic and Celtic tribes.
In cooking, Beer can be used to make a frying batter, or to flavor beef, rabbit or game dishes. To cook dried salt cod, salmon, shellfish and crustaceans. Or, even, to soak fruit cakes.
Fun fact: in Middle Ages, when plague spread, Beer, was among the few healthy beverages (together with other fermented beverage with boiling among the production steps). River waters, actually, were full with germs and pathogens. Once they discovered this characteristic, many Countries started depuring drinkable waters.