Note: Microsoft Equation Editor 3.0 isn't supported in Office 2016 or 2013.
You don’t need to install anything to write or edit math equations in Microsoft Word 2013 or Word 2016. Just choose Insert > Equation.
Equation Editor (Microsoft Equation 3.0) was included in previous versions of Word and is still available in case you need to edit an equation written in a version of Word older than 2007. Double-click the equation you want to edit, and the equation editor will open automatically.
Important: This feature isn’t available in Office on a Windows RT PC. Want to see what version of Office you're using?