Kind of a late response to your question, but in case anyone else needs an answer: you need to enter to the survey details page and press the "Begin Survey" button.
Extracted from the Begin Survey page:
Click Begin Survey to change the survey state to active. This allows respondents to fill out the questionnaire. Once active the survey can no longer be edited. It is not possible to return to design state. For this reason it is a good idea to test the questionnaire first using the Begin Testing button.
When enough responses have been received the survey can be completed using the Complete Survey button on the Survey Details page. The Auto Complete option can be used to automatically complete the survey when the criteria is met.
Respondent status can be monitored and additional respondents added by clicking the "Manage Respondents" button from the Survey Details page.