First select your cells and go under Home tab into Styles section. Choose the first button from the row called “Conditional Formatting”. From there choose “Top/Bottom Rules” and “Below Average …” From the appearing menu select the style you wish to apply. Notice that some only apply to text or background whilst others format both of those. If you are satisfied, click on “OK”. 

First select your cells and go under Home tab into Styles section. Choose the first button from the row called “Conditional Formatting”. From there choose “Top/Bottom Rules” and “Above Average …” From the appearing menu select the style you wish to apply. Notice that some only apply to text or background whilst others format both of those. If you are satisfied, click on “OK”.