The U-Bahn and the S-Bahn

The transportation system of Berlin is very comprehensive, clean, reliable and affordable. The U-Bahn (underground/subway) system is easy to use if you are used to the subway systems in other major cities such as London or Paris. There are bus and tram lines too. When switching trains sometimes the train you want is just on the next platform and not up a level or down a level, making it even easier to change trains. The trains cover most of the city. The only part that is not covered well is the Tiergarten area. The Hansaplatz  station will let you off near the Star and Victory Column and then you can walk through the park.  The Eyewitness guide for Berlin has a full map for easy reference. 

The S-Bahn (above ground train) system is also good. There are points where you can change from the Ubahn to the Sbahn to help you get to your destination. At the Yorkstrasse station you must exit the U-Bahn and then just go up the street a very short distance to the S-Bahn station.

There are no ticket takers at the U-Bahn stations. There are machines that will allow you to purchase tickets for the day, a few days or 7 days. The prices vary depending on the number of days or the distance you need to travel. The city is divided into A B and C zones. The 7 day ticket for all three zones was 32 euro. The machines will accept coins and bills of 5 or 10 euro only. The machine also allows you to change language. The honour system rules on the trains. There are no ticket takers and no turnstiles. You must  validate your  single ride ticket in the machine next to the machine that sold the ticket and be able to produce your ticket when asked for it by undercover, transit staff. If you do not have your ticket, the fine is quite heavy - we saw several inspectors in a short city break, don't even think about risking it (40 Euros in 2015). Tickets for more than a day must be validated only once to show when it ticket became active.

As there are no ticket takers in the stations, if you have a problem, then you must then rely on the kindness of strangers. Many people speak English and also the use of hand gestures and pointing to the station you are trying to get to will help the native Berliner show you which train to take. The most difficult station was Potsdamerplatz. There is a U-Bahn and S-Bahn station there but again there are no personnel there. It is not unusual to find groups of tourists here, apparently lost, looking for help and no one to help them find the train they need. The signage here could definitely be improved.

Tourist maps don't help a great deal as they usually don't have the U-Bahn line number shown and are also very small so difficult to read. The best we found in a tourist information office was issued by the BVG, responsible for urban transport, that has a folded A3 transport map and an A4 general map of central Berlin only.

There is a sign in the ubahn station platforms to tell you which train route is using the platform, the direction the train is going (the final stop on the line) and how long it will be before the next train arrives.  

Rush hours are not crowded on the U-Bahn. There are many bicycle lanes beisde beside the sidewalks and many people also live fairly close to where they work, so the trains are not overloaded. Even if it is not possible to get a seat there is plenty of standing room.

On working days U- and S-Bahn close at around 1am but there are buses that take over to cover the night hours until the next morning's reopening. On weekends all U-Bahns (except U4) run every 15mins all through the night plus the night buses as above. On weekends all S-Bahns run at different intervals all through the night.

Links:

Both U-Bahn and S-Bahn are one system as far as ticketing is concerned but they are run by different transport authorities.

U-Bahn, Buses, Trams and Ferries = BVG
S-Bahn = Deutsche Bahn

However, you can usually forget about this fact. When you buy tickets - all tickets are valid for all modes of transport within the zone you bought. And if you do a search on the BVG site, the result will include all modes of transport - U-Bahn, S-Bahn, Bus, Tram and Ferry.

All service info - BVG: http://www.bvg.de/index.php/en/Bvg/Start