So, first, you obviously already know that Germany is famous for its beer. German brewing is rooted in tradition and history, and Germans are extremely proud of their beer. What that means is that tradition, and the "perfection" that has been attained from hundreds of years of brewing a specific beer, is the most important thing. So although these beers may seem rather simple, or non-innovative, to the micro-brew connoisseur (don't expect any really great IPAs or chocolate stouts or such), the key is that they are consistently good. German beer is regulated by law, and although it is not as strict as it used to be, the German Beer Law allows only a limited number of ingredients, mostly just water, barley, hops, and yeast. So no crazy things like chili peppers, coffee, or chocolate.
When ordering a beer in Bavaria, all you need to decide is which style of beer you want: a pale beer (Helles), a wheat beer (Weißbier), a dark beer (Dunkles), or if you don't really feel like drinking a lot, perhaps a Radler (a mix of beer and sprite). That's it. You say, "ein Helles bitte", and then the waitress will bring you whichever Helles that establishment happens to have on tap. Helles is the most common beer ordered in Munich, although most beer lovers from outside Germany, when visiting, prefer Weißbier or Dunkles. In some places, you may also have the choice of choosing between a liter (ein Maß) or a half-liter of beer, although in many places that is also not a choice, and you just get the size that you get.
Many of the towns across Bavaria have breweries, often even monasteries where the monks have brewed for centuries. In Munich, the six big breweries are: Hofbräu, Löwenbräu, Augustiner, Paulaner, Hacker-Pschorr, and Spaten. Restaurants and beer gardens will be affiliated with one of those breweries and will serve only, for example, Augustiner beers. Locally, Löwenbäu and Spaten probably have a reputation for being the "lesser" of the breweries, although that is of course debatable depending upon individual tastes, but if you are looking for the best of the bunch, I would suggesting defaulting to Augustiner. There are also other smaller breweries from the Munich area with beers that are commonly served in Munich, e.g. Andechs, Erdinger, Schneider- Weisse, etc. These beers tend to be excellent.
So these are just some of the very basic details on Munich beer, but they're all important things to know when breaking into the beer culture here. The way to learn about German beer culture is not by doing any fancy beer tastings or perusing lists of micro-brews (both of which activities I myself greatly enjoy and look forward to when visiting friends and family out in the US), but by simply visiting the different breweries and beer gardens in the region, and ordering a Maß of whatever they have on tap.