An election is where you vote for a governing body (Government or local council) to be "in power" for a set legnth of time. Eg a general election
A referendum is a single vote on a single matter to decide it once and for all. Example of this would be Joining the EU in which a yes vote was entered by more people than no. So Britain is now in the EU and a periodic vote need not take place to keep us there.
You also have the fact that with a referendum there is proportiaonal representation - ie if 51% of people vote yes, it goes through - in an election you can have the ludicrous situation that a lower percentage of people around the country voted for the governement as oposed to the opposition but the governement is elected as they gained more constituencies.