Office has equations that you can readily insert into your documents. If the Office built-in equations don’t meet your needs, you can edit, change the existing equation, or write your own equation from scratch.
To type an equation from scratch, press Alt += on your keyboard.
Choose Insert > Equation and select Insert New equation from the bottom of the built-in equation gallery. This inserts an equation placeholder where you can type your equation.
Add an equation to the equation gallery
Select the equation you want to add.
Choose the down arrow and select Save as New Equation....
Type a name for the equation in the Create New Building Block dialog.
Select Equations in the gallery list.