No less than four languages are spoken in Switzerland: German, French, Italian and Rhaeto-Romanic. Swiss people working in tourism usually speak English as well. The great number of languages spoken in this relatively small country can be explained when looking at the history of Switzerland.
The majority of Swiss people speak German. German spoken in Switzerland is also called "Schwitzerdütsch", or "Swiss German". Don't expect to understand Swiss German if you understand standard German as it's spoken in Germany. It sounds totally different. Swiss German has its own words and a very different pronunciation. Some examples of typical Swiss words are grüezi (hello) and grüezi miteinand (hello all together). German people will not greet you like that. On top of this, there are different dialects per region.
Even though Swiss German is very different, you can speak standard German and most Swiss people will understand you perfectly fine, and will adapt so you understand them better.