Schema Pro allows you to accept user ratings which are then calculated together and the aggregate is displayed in your snippet.
You can accept user ratings for the following Schema types
- Local business
- Software Application
In order to accept ratings from users and display the aggregate in search results, you will need to select the Accept User Ratings in the dropdown menu.
When selected, this will display stars in the front end through which users can rate the page/post. This is how the stars will look like in the front end.
This is then considered and the aggregate is calculated to display in search results.
The following image shows how this field will look in a meta box added to the respective page /post edit page. If you are the admin and need to edit ratings, you can reset them here.