Alcoholic drinks are frequently used as ingredients in recipes. This page lists the most common types used as ingredients. See the Bartending book for mixed drink recipes and other topics relating to direct uncooked consumption of alcoholic drinks.
Small amounts of alcohol can be useful for cardiovascular reasons and blood sugar. Harvard says "For men, a good balance point is 1 to 2 drinks a day. For women, it's at most one drink a day." The USDA agrees, while also stating that women of childbearing age who are planning to become pregnant should completely avoid alcohol. Also, since ethyl alcohol turns to sugar in the bloodstream, it helps regulate blood sugar. See the warnings listed below though, while being aware that many people have difficulty keeping consumption moderate.
Beer is any variety of alcoholic drink produced by the brewing process: fermentation of starchy material derived from grains or other plant sources, such as malted barley or wheat. Beer typically has an alcoholic strength of from 3 to 8 percent. However, certain Belgian and independent craft brewers produce beers with alcoholic strengths in excess of 8%, with 12 % not being uncommon for these styles.
Throughout most of the World cider is the fermented juice of apples (there are special cultivars used for cider making). In the USA cider normally refers to unfiltered unfermented apple juice and the alcoholic variety is known as "hard cider". Cider, like beer, typically has an alcoholic strength of from 3 to 8 percent.
Perry or pear cider is an alcoholic beverage made of fermented pear juice. It is similar to cider, in that it is made using a similar process and often has a similar alcoholic content, up to 8.5% alcohol by volume.
Wine usually has an alcohol content of between 10 and 15 percent, and is made by fermentation of grape juice. Fruit wines are wine-like beverages made from fruits other than grapes. Fortified wine such as port and sherry is made by adding brandy to wine, increasing the strength to around 20 percent.
Mead is an alcoholic beverage made of honey, water, and yeast. It is roughly of the same alcoholic strength as wine, and is sometimes known as "honey wine". Before import of grape wine became economical, mead was very popular in Northern Europe, including the British Isles, Poland and Scandinavia. In Viking Age Scandinavia, mead was considered to inspire skaldic poetry. Mead is probably also the origin of the word honeymoon as the father of the bride was said to give as a dowry a month's supply of the liquor.
The term spirits includes brandy, cognac, rum, vodka, gin, vermouth, and whisky; other spirits are not widely used in cooking. These are made by distilling weaker drinks to concentrate the alcohol content to 35 percent or more. Spirits are often used in dramatic formal flambe desserts, where a very high concentration of alcohol is required to allow ignition.
Excessive consumption of alcohol may cause loss of social inhibition, vomiting, and a hangover. In extreme cases, alcohol poisoning may occur, which can be fatal. It is known that excessive use for a prolonged period of time can cause liver diseases like cirrhosis, and may even alter brain functions.
Intoxicated people should not operate heavy machinery, including automobiles. Pregnant women should avoid alcoholic beverages, to prevent damage to the fetus (Fetal Alcohol Syndrome).
Consumption is submitted to extensive regulation in most countries. In particular, a person not of legal drinking age who consumes alcohol may face legal troubles (along with their guardians, and/or those responsible for supplying the alcohol).
See also 
Bartending, the Wikibooks Bartending Guide