This screen lists all students currently enrolled in the course you selected.
If you wish to send email to members of this class, you have two options (listed at the bottom of this screen):
De-select All: Use this option if you have a large list and wish to email only a few students. This will clear the checks out of every box and make it easier to select the few you desire.
Select All: This option allows you to put a check in every box. If you messed up your list and wish to start over with all of the boxes checked, choose this option.
Once selecting the members you wish to send email to, simply click the Mail to Group icon.