Top fermenting yeast, which is used to make ales, earns its name because it has a tendency to ‘flocculate’, meaning it gathers at the surface of your beer before sinking to the bottom. Ales need warmer temperatures for the yeast to kick into action, multiply and make themselves delicious. With a higher alcohol content, they usually pack more of a punch than lagers. With beer and humans comes experimentation, so variants of ale include brown ales, pale ales, mid ales, old ales and bitter, which is a kind of well-hopped pale ale.
Lager yeast on the other hand is bottom-fermenting. So, like a well-trained ballerina it performs a simple flocculation (not rising to the top) and sinks to the bottom. Originally invented by the Germans who stored their beer in ice caves during summer (German engineering!), lagers are still made at cooler temperatures and have less alcohol making them easier-drinking beers. As a result they are more widespread. Think of them as the popular girls. Castle Lager is a prime example of a great lager served cold.