OK, so briefly I've discussed lagers and ales, so let me go into a bit more depth. Lagers are a German (and Czech) invention that use a species of bottom-fermenting yeast to create the beer. The yeast only do their thing at cool temperatures, so the result is a simpler, crisper beer. The common "macrobrews" of the U.S., Canada, Australia, and Mexico are all lagers, and specifically are pilsners or their close relatives. They are all easy drinking, which is why they have become so popular. Another somewhat easily found group of lagers are the bocks (bock, eisbock, doppelbock, maibock, and helles bock). These have more complex flavors and aromas than pilsners and their relatives, but are still rather crisp.
Ales, on the other hand use a top-fermenting yeast species to create beer. This can be done at warmer temperatures, allowing more complex esters to form in the beer. These beers have a greater depth of flavor and are typically "heavier" and more robust. Ale styles are far more numerous than lager styles. Stouts, porters, pale ales, IPAs, ESBs, browns, wheat beers, Hefeweisens, and the fine array of Belgian ales are just some of the styles you may encounter and cover the range of light and refreshing to robust and heavy.
Both lagers and ales are beer. Don't let anyone tell you they don't drink beer, only ales (or lagers). They are both beer. Period.
