Using credits to get responses
So you have some credits, but how do you get respondents?
Simple, you don't have to actively use them. As long as your survey status is 'online' your survey will automatically collect responses.
The survey above costs 1 credit per completion. As long as this user has 1 credit or more, it will be online.
Pausing a survey
If you want to, you can also pause your survey, by clicking the settings button beside the 'online' box and clicking 'pause'.