You can toggle the status of your survey between Closed and Live by using the link in the Status column of the My Surveys page:

Note that Closed surveys can only be taken Live if they have previously been launched at least once. Any Live survey can be toggled to Closed but you will be prompted to confirm when you click on the Live link, to ensure you don’t accidentally close a survey you did not intend to close.

For more information on launching a survey, click here.