How to insert an equation with fractions, square roots and exponents
How to add an equation in your document, see Working with Microsoft Equation.
To insert, for example, the normal distribution, or Gaussian distribution, do the following:
1. In the Equation Editor enter f(x)= and then select Full-size vertical fraction in the Fraction and radical templates group on the Equation toolbar:

2. Enter 1 in the top of this template and in the bottom choose Square root in the Fraction and radical templates group on the Equation toolbar (to move the cursor around in an equation by using the keystrokes, see Keystrokes for Moving the Cursor within an Equation):

3. Enter 2 and then choose in the Greek characters (lowercase) group on the Equation
toolbar:

4. Select Superscript in the Subscript and superscript templates group on the Equation toolbar:

Enter 2 in the Superscript field.
5. In the left of your formula enter e, choose Superscript and then enter "-" and choose again Full-size vertical fraction and Superscript to finish your equation:

How to adjust spacing and alignment in an equation, see Adjusting spacing and alignment in an equation.