To add a Product, you can:
There are 2 options next to "Add Product" button:
To analyze the feedback collected on your surveys, go to Analytics >> Dashboard.
You can create widgets in on the dashboard based on the questionnaire where you can use Product as a base to create a few widgets like NPS List and NPS Trend Comparison whereas for all other widgets you can use Product as a filter
Below are the examples of how you can use product in your analysis: