Beer is a beverage made from fermenting wheat products into a drinkable concoction of anywhere between 0.5 % and 20% alcohol. It originated in Mesopotamia about 5000 years ago, and from there spread north into Europe, where beer is often most associated with. Societal interpretations of beer have changed over the years, and although in Northern European contexts is considered the more manly drink, in Ancient Greece it was actually only a drink for women. Wine was the choice of drink for men, instead. Beer comes in many different varieties depending on region. I'll go over some of the basic ones, including Lager, Ale, Stout, and Weissbier (Wheat Beer). The differences mostly come in the brewing process, which can greatly affect the colour and flavour of the Beer.
Lager- This is probably the most common kind of beer found in the United States, and is what companies like Budweiser, Heineken, and Molson specialise in. It is the most popular kind of beer in the world. Lager is characterised by being made through cold fermentation, and was traditionally made in the winter, and drank in the summer.
(Moosehead Lager [or Moose Green colloquially] a lager brewed in my region of Canada)
Ale- These are often what can be found in craft breweries, but also have a tradition (chiefly in the British Isles) going back centuries. Ales are made with yeast which ferments it quicker, and results in higher alcohol content, and a darker colour (with the exception of IPAs or Koelsch type beers). These were the opposite of Lager, and were brewed in the summer for consumption during the winter.
Stout- These are very dark beers originating in Britain. The most famous of these is Guinness. These are characterised by a very dark colour, which although appearing black is actually a very, very dark red.
Weissbier- A very common style in Bavaria, and Belgium. These use a lot more wheat than malted barley, and both German Weissbier and Dutch Witbier mean "White Beer" etymologically. Paulaner is a prominent brand of Bavarian Weissbier.