Check boxes can be used to select an email or emails on which you would like to perform an action.
1. Go to the email account desired.
2. Select email or emails that you would like to perform, actions such as "delete", "archive" or "flag" on by clicking on the empty box on the left of each email. ("More Actions" can found on the top right side of the email, represented by three vertical dots. Clicking on More Actions will show a drop-down list of all the actions you can perform on the email.)
Note: When you select an email, the check box on the left will turn pink with a white check mark inside.