If you are a citizen of EU/EFTA member states, you have the right to temp in Switzerland. You can work without a residence permit for up to 90 days in a calendar year. More than that, and you will need a contract of employment in order to register yourself and obtain a permit.
For citizens of countries outside the EU/EFTA who don’t already have an existing, valid permit, employers must apply for a work permit on your behalf before they can hire you.