how can I travel from Berlin to Saarbrucken by Train? and How much is it?

Scroll down your page to the flags. Click on the German flag and ask your question there for an accurate answer. They will be happy to tell you. The rail system in Europe is universal and always on time especially in Germany. Have fun.

Well assuming it is at the weekend and you want the cheapest fare, on local trains 33 euros:

Station/Stop Date Time Platform Products Comments
Berlin Hbf Su, 30.12.07 dep 08:13 14 RE 38012 Regional-Express
Number of bicycles conveyed limited, SnackPoint/Snacks on board the train, vehicle-mounted accessaid, notification: 01805-512512 *, (*14 ct/Min. aus dem dt.Festnetz via Arcor, Mobilfunk ggf. abweichend)
Magdeburg Hbf Su, 30.12.07 arr 09:53 8
Magdeburg Hbf Su, 30.12.07 dep 10:11 3 RE 36085 Regional-Express
Number of bicycles conveyed limited
Sangerhausen Su, 30.12.07 arr 11:39 4
Sangerhausen Su, 30.12.07 dep 11:46 4 RE 26156 Regional-Express
Number of bicycles conveyed limited
Kassel Hbf Su, 30.12.07 arr 13:53 11
Kassel Hbf Su, 30.12.07 dep 14:23 9 RE 4111 Regional-Express
Number of bicycles conveyed limited, vehicle-mounted accessaid, notification: 01805-512512 *, (*14 ct/Min. aus dem dt.Festnetz via Arcor, Mobilfunk ggf. abweichend), air conditioning
Frankfurt(Main)Hbf Su, 30.12.07 arr 16:34 14
Frankfurt(Main)Hbf Su, 30.12.07 dep 17:08 20 RE 4370 Regional-Express
Number of bicycles conveyed limited, vehicle-mounted accessaid, notification: 01805-512512 *, (*14 ct/Min. aus dem dt.Festnetz via Arcor, Mobilfunk ggf. abweichend), air conditioning
Mainz Hbf Su, 30.12.07 arr 17:50 3 a
Mainz Hbf Su, 30.12.07 dep 17:55 2 b RE 3340 Regional-Express
Number of bicycles conveyed limited, air conditioning
Saarbrücken Hbf Su, 30.12.07 arr 20:12 16
Duration: 11:59; runs not every day, Days of operation
Hint: Departure/Arrival replaced by an equivalent station Fare: 33,00 EUR

www.diebahn.de (also in english) gives you the answer. If you got a lot of time, you can use the "schoene Wochenende Ticket" (Nice weekend ticket) and travel for something like 29,00 € from Berlin to Saarbruecken.Otherwise, it depends on the time of day, prebooking, class of service, type of train. Better look it up in the pages above.