Lager is beer. Beer is either ale or lager. Ales are made using top-fermenting yeasts and don't take long to make. Lagers are made with bottom-fementing yeasts and (traditionally at least) are stored after the main fermentation at cold temperatures for a period of time.

Let's get one thing clear. The vast majority of bottled ales and lagers are pasteurised and there is no yeast in the bottle. Their flavour is drastically altered by the process. Try comparing bottled London Pride or Doom Bar with the cask-conditioned versions. Completely different drinks, yet they were brewed the same way. I'm used to drinking cask-conditioned ale in pubs and I can't be doing with bottled ales unless they are bottle-conditioned, i.e., not pasteurised or artificially carbonated. Bottle-conditioned ale has yeast in the bottle. I don't go for draught lager so I'm fine with bottled as long as it's good stuff, but only on hot summer days. I like CruzCampo when I'm in Spain and Peroni in Italy (or here). There's a very nice Spanish one called Alhambra. We had some lovely ones in Prague but I can't remember their names (I think one was called Bernard!). Most supermarkets sell a Belgian wheat beer called Duvel for about two quid the 330 ml bottle. It's bottle-conditioned at way over 8% and is just about the best beer you'll ever taste. Pour slowly and drink the dregs from the bottle. Trust me. Treat yerself, but go easy!