Over 4.5 million people a day use the DB's 29,000 trains serving over 5,500 stations along 35,000 km of track.
The Deutsche Bahn was formerly a government corporation but is now completely privatized (although it is still owned entirely by the government.) It was created from the old West German Deutsche Bundesbahn (German Federal Railways) and East German Reichsbahn (Imperial Railways).
Eurail passes are created by a European train carrier-owned consortium called Eurail, which sells European train passes to non-European citizens through various sellers.
If you’re a European citizen, you will need an Interail Pass instead.
There's one other important plus with the S-Bahn which is that you can use the main rail passes on it (but not the U-Bahn), but we'll get onto that later.
Both S-Bahn and U-Bahn run frequently, especially as you tend to find you can take one of several lines to go to most places in the core of cities (and they group them all together on one platform! Although the S-Bahn networks do often extend into the immediate area of the main cities, as a general rule, if you want to go between different cities & towns, you're going to be using the main railways, Deutsche Bahn.
I got around exclusively on trains when in Germany, and so will you, coz it's environmentally sound, all the cool kids are doing it, and it's almost fun. (This is a good example of how in German words get stuck together to make other words – which is good because there's less to remember, and you can often make a guess at unfamiliar words if you know part of them.) The U-Bahn and S-Bahn are what you use to get around in the cities.
Personally, I almost never used the U-Bahn – if I was only going for a very short hop, I'd just walk, and the S-Bahn nearly always stopped often enough to get close to where I was going.
While tickets booked "last minute" can be expensive, a bit of planning can make tickets surprisingly cheap.
Despite the rise of Intercity buses in Germany, trains are still the main mode besides cars for travelers to get around.
This comprehensive post intends to go from the basics of acquiring your pass to getting the most for your money.
It is not only based on hard guide facts, but also from my experiences and mistakes.