Go to: My Surveys (Select Survey) » Edit
When you enable Global Password Protect option, there is one common password for the respondents.
Because this is a global password it will be same for all the respondents. You can make the password a part of the email body when you send it to the respondent.
To include the password in the email invitation, goto:
Login » Surveys » Send » Compose
This feature is available with the following licenses :