The Invisibles command shows or hides hidden characters such as carriage returns, spaces and tabs, which can be helpful in spotting formatting errors.
To show invisible characters, on Mac go to View > Document > Show Invisibles, and on Windows go to View > Show Invisibles.
Text with invisible characters shown:
The paragraph marks 
indicate hard carriage returns (inserted by the user) and the small dots indicate hard spaces between words (inserted by the user).
To hide the invisible characters on Mac, go to View >Document > Hide Invisibles, and on Windows, View > Hide Invisibles.
The color of the invisibles can be changed under Document > Page Layout > Colors.