Google Opinion Rewards is an app developed by the Google Surveys team that enables you to earn Play Store credit (which you can use for other paying applications) simply by answering surveys.

How does the Google Opinion Rewards app work?

After downloading the app, you will be required to answer basic questions about yourself so that Google can cater the surveys they send you to your tastes, habits, and interests. From that point on, you'll usually receive one weekly survey, although the frequency may vary from time to time. You'll get a notification on your mobile when you've received a survey to answer. After completing it, Google will credit your Play Store account or a PayPal account with approximately $1 per survey.

The number of surveys you receive depends on both your location and the shops and establishments you go to so it's a good idea to have your GPS activated. The questions included in the surveys are usually commercial or about your habits and tastes and the surveys take on average 20 seconds to complete.