The first thing you have to do once you download this tool is answer a few basic questions about yourself. Google uses this information to send you different types of questionnaires. Depending on your answers, the app sends you questions once a week, although sometimes it can be more or less frequently.
When there's a questionnaire available, you receive an alert telling you that you can fill it out whenever you like. Not all the questionnaires offer free credit, but in the best cases you can receive enough to purchase something from Google's store. There are all kinds of questions, keeping things interesting. When you have enough to buy the game you want, you can get it directly from Google Opinion Rewards.