In general, when traveling in Germany and other German-speaking countries, like Switzerland and Austria, diners should not wait to be seated. They should directly go to an empty table and sit down. In very expensive restaurants, there may be someone who will seat diners.
Nothing Is Included In Your Meal
As is the case in much of Europe, your meal comes with nothing. If you want tap water, you must ask for it (though expect your waiter to be horrified that you would drink tap water.) More likely, if you ask for water, they will bring you a bottle of mineral water.
Similarly, you should expect to pay for any bread brought to the table. Bread is not free (and often is relatively tasteless, so I often skipped it at restaurants.)
Even at fast food restaurants, expect to pay for anything extra. For example, you'll be charged for ketchup when you order fries, even at McDonald's.
Paying at German Restaurants and Tipping
A German restaurant bill will include several additional charges beyond the food itself. First, a 19% value-added tax (VAT) is included on the price of most things purchased in Germany, including on all restaurant bills across the country.
Second, most restaurants include a 10% service charge which is used to pay for the busboys, front desk staff, and for broken dishes and cups. The service charge is not a tip for waiters, which is why you should add about 5 to 10% above the service charge.
As in much of Europe, German restaurants do not always accept credit cards.
It is definitely the norm to pay by cash. The waiter will stand next to you and hand you the bill. You should respond by telling the waiter how much you want to pay, by adding a 5 to 10% tip to the total bill, and he/she will give you change. This tip is called a Trinkgeld which translates to "drinking money." Do not leave the tip on the table, as you would in the United States.
For example, if you go to a restaurant, you would ask the waiter for the bill by saying, "Die Rechnung, bitte" (the bill, please). If the bill arrives with a total amount of 12.90 Euros, you would tell the waiter that you want to pay 14 Euros, leaving a tip of 1.10 Euros, or 8.5%.
That being said, if you are in a small coffee shop or order a small meal, amounting to no more than a few Euros, it is perfectly acceptable to round up to the next highest Euro.