The Rating by Source widget displays the average rating from each source your client got reviews on.
In the "Social Review Sources" setting, you can check and uncheck to show the data from the following sources: Facebook, Google, Indeed, Instagram, Just Dial, Mouthshut, Trip Advisor, Trust Pilot, Twitter and Yelp.
The "Social Review Types" setting allows you to set the type to Social reviews, Corporate Buzz, or both.
While hoovering over a bar will show you the amount of the reviews, clicking on one will open a pop-up, displaying the review details.
Clicking the View link on the right side of the row will open an original review left by the reviewer.
The "Review Text" setting allows you to enter a keyword(s) and display only the reviews containing the word you want to focus on. Drilling down through a widget set up like that will also show reviews only with the selected word.
Remember to check a different help article detailing other settings of this widget.