Hi there, Igor!
Don here from Shopify. :)
Apps like this will often require you to make some coding edits to your theme first and import reviews to your store in some way.
Have you checked within the app in your Shopify admin to see if there are instructions there from the app developers on what you need to do next?
Try checking there for any specific instructions on what you need to do next for this app and if you can't figure it out at all you can still reach out to the app developers for support.
Just use the contact details here on the app store page to get in touch with the developers of that app who will be able to guide you through installation and using their app.
All the best!