Municipal, cantonal, and federal referendum are periodically scheduled (weekly, monthly, quarterly and yearly) on any topic. The purpose is to counter-balance the powers of elected representatives via a permanent checks and balance system. See Article 23 and 23-Bis of the constitution.
Electing municipality members is done once for a certain period of time (say a 4-year term mandate).
However, when the municipality board takes a decision that affects the wellbeing of the local citizens (sewage treatment, garbage collection, painting the houses of a village, etc..) then residents of the municipality might submit the decision to a vote (votation) if they are not in favor of this decision.
You elect once but you vote every time on any controversial decision taken by the elected executives, each time a proposal for votation or referendum is submitted on any given topic.