If transportation budget is a main consideration for you, then you will probably want to take the metro, Berlin’s cheapest and most economical means of transportation.

The U-Bahn
The Berlin metro is one of the best in the world, and is composed of the two systems, one of which is the German U-Bahn, the main metro system in Berlin.
Eighty percent of the U-Bahn is underground and spans a total of 151.7 kilometres or 94.3 miles. Because of its large scope, layout and strategic placement all around the city, you can be sure that there is a station near every major landmark or tourist destination you wish to go to. And you can enjoy a short walk from the station to wherever it is you’re going to – everyone needs a bit of exercise every now and then.
The U-Bahn has trips every day, increasing the frequency of train trips during rush and peak hours – there’s a train in a station every four minutes. During regular hours, the wait becomes five minutes. On Sundays and evenings, there’s a ten minute interval for trains in the metro. Berlin is also experienced in a different way through the U-Bahn, as you get to see Berliners go about their business during ordinary days, and the rapid train transport system takes you away from traffic jams and pollution outside, and train schedules can help you time your trips and itineraries better.

The S-Bahn
Besides the operator, there is no difference between the S-Bahn and the U-Bahn. The former is a smaller system operated by a different outfit, but is also integrated into U-Bahn system.
Not to worry though, as the whole Berlin metro comprised of the U-Bahn and S-Bahn are a completely unified system, so there’s no need for separate metro passes or anything.
The System as a Whole
The metro Berlin train system serves as the main means of transportation for most Berliners, as it is the most economical and practical way to traverse the bustling city without running into obstacles like traffic jams or road repairs. Tourists on a budget are known to frequent Berlin’s metro lines, as it is the cheapest way to go around the city and has stations located virtually near every major destination in Berlin.
One precaution though, is to bring a German dictionary with you so you can ask for direction properly if you happen to encounter someone who isn’t well-versed in English. Most Berliners, as well as the staff of the Berlin metro, will be happy to help you out though, so there’s little reason to be anxious at all. You may even learn a little German in the process – and that’s a good thing, right?