Legal Moves
Why are there dots on certain squares when you click on a piece? These dots highlight all the legal moves for that piece. This feature is enabled by default for new accounts, but you can easily turn it off if you prefer.
Web
Click 'Settings' from the bottom-left menu of any Chess.com page.
Select 'Gameplay' from the settings menu and toggle the 'Show Legal Moves' option to your liking.
Click 'Save' to apply the changes.