Hello... Are Euros commonly used throughout?
No, they use Swiss Francs. You can pay for things in Euro, but the exchange rate is maybe not quite the best and you get your change back in Swiss Francs.
As Sam mentioned, currency in Switzerland is the Swiss Franc and while some merchants or hotels may accept Euro, the exchange rate offered will generally not be too favourable. If you withdraw funds from an ATM, CHF will be provided.
And those francs will FLY out of your pocket quicker than you can imagine. Everything in Switzerland is wayyy expensive.