For an American to arrive and go into a pub or restaurant in Germany....there's this awful gut feeling over what exactly you should try for liquid refreshment. So I will offer you these tips.
First, Coke is generally always available, along with Fanta (the German version of Mountain Dew), and a diet drink. The odds of getting Pepsi? Less than five percent of pubs might carry it. So get used to Coke. Now the gal will ask you....if you want the smaller glass or the larger one, so you might want to pause and think for a minute over that. I'd advise the larger one, if you are going to eat something.
Second, water. Leitungwasser is just plain tap water. You can ask for it, but the pub gal will look at you and think you are a nut. So I'd advise one of the other two varieties: Mineralwasser (water with bubbles or minerals to it) and stilles wasser (glacier water or spring water). The issue with these two is that it will cost you a buck or two for a bottle. If you are thirsty, then ask for the bigger bottles, but expect to pay $4 roughly. If you haven't had water with bubbles before....then I'd strongly advise you to take stilles wasser instead. How many Germans will order a bottle of water on an evening meal? Maybe one out of fifty.
Third, wine. Every menu has several options: red wine (rotwein), white wine (weisswein), Italian wine, French wine, German wine, etc. There's also the size business....where you order just one glass, or get a wine container with enough for two glasses (typically for a couple or just a guy who likes two glasses of wine per evening). The one key thing you can count on.....most everything they serve will be dry wine. So if you dislike dry wine....gaze over the menu carefully....to pick something else. Typically, you can't get drunk off one glass of wine. If you sit there for three hours, consume a meal, and drink four glasses of wine....you probably shouldn't be driving. So walk back to the hotel, or stop the wine at two glasses.
Fourth, beer. Well...there's lots of options here. Bock beer is rich black beer and fairly strong (stout), with Doppelbock being twice as strong and stout. (note: a Doppelbock can have up to sixteen percent alcohol in it, and you ought to limit yourself to strictly one beer). Neither ought to be consumed by a person who rarely drinks beer. Then you have ein helles beer, which is a light beer. Then there's Weizenbeer, which is a wheaty-tasting beer. A Pilsener beer is generally a good choice to pick from.....neutral in all categories, and generally around 4.5 percent alcohol. An "export" beer is also generally a good pick in all categories. An Altbeer is generally a dark beer which is brewed to English expectations, and it's fairly bitter in taste. Finally, there's Hefewizen beer, which is very wheat-tasting in nature.
Fifth, coffee. What you should expect is a strong brew of coffee, perhaps a step above what you get at Starbucks. Germans like strong coffee.
My general advice is to consume plenty of water during the summer months....maybe order yourself a small bottle of glacier water, and have a beer after that. You need to stay hydrated during the hot summers. For the fall and winter, you might want to have two beers with your meal, and finish up at the end with a cup of coffee.
If you really aren't sure about what to drink....just order up a bottle of water, and maybe one small glass of wine to go with the meal. You can't go wrong with that.
Finally, there's this issue with buying beer in a one-liter stein. Frankly, if you go and do this.....it's a good bit of beer....way more than most Americans are used to consuming. Sadly, you might get stupid with the stein of beer....drink most of it before the meal arrives, and then ask for a second one-liter stein. That....is way more than you should consume. And you will be drunk by the end of the second stein, if you don't spread this out over three hours.