A while ago, I was in a restaurant with a few English friends, and at the end, when there was the bill to pay, there was a bit of confusion as to how tipping is done in Germany.
Just in case you are wondering about that now - it's done in a kind of reverse haggling. The server adds up what you owe to the restaurant, then you hand over the money and say a number that is a bit higher - depending on how much you want to tip. The guideline is to add about ten percent if you were happy with the service, but in practice, Germans often round up to a full Euro in about that range (which means, with small amounts, there can be server-friendly prices and not so server-friendly prices). Leaving a tip on the table is not an usual practice here.
So, for instance, the server tells you "Eighteen fifty", and you say "twenty" and hand over that 50 € note, getting back thirty Euros. Alternatively, you can of course give your server a 20€ note and say "stimmt so" or "Danke" - the latter can possibly lead to misunderstandings if you are just trying to be polite when handing over the money!
Austria has similar tipping practices, as has Switzerland, at least as far as I know. I still remember being in a country where it was customary to leave the tip on the table for the first time - it was really weird and confusing for me!