Customer satisfaction report shows how many closed conversations were rated Great by your visitors/customers. Chat rating is shown to your visitors/customers automatically after the conversation closure. You can disable the chat rating via Settings → Chat Rating.
Note that, If your satisfaction report is flat, it might be due to not closing conversations. Also, there might be no chats during the selected time period.
By clicking each metrics, you can see the exact chats rated and can follow-up with your customers to get better results.
You can also export the list of chats to a file, bulk-apply some tags or statuses...