As you can guess by its name, the Most Popular Quiz shortcode is meant to display the most popular quiz on the front end, which was passed the most times by the users.
To use it, go to the General Settings > Shortcodes and find the corresponding shortcode.
Copy and paste it into a new post or into an already existing post.
Now, publish your post or update it. Click on View Post to see the result.
This is an example of a list of the most popular quizzes.
Here is a quick video tutorial on how to set the Most Popular Quiz shortcode with the plugin.