Teachers can send messages to students, and vice versa, but students are unable to send messages to other students.
To send a message:
Click on the person icon on the right hand side of the top bar
On the drop down menu that appears click on 'Messages'
You can choose to send either a message to the whole class or to an individual person
To send a message to the whole class click on the name of the class which will appear on the menu on the left hand side of the page. Type your message in the box provided and click 'Post Announcement to [class name]'
If you want to send an individual message then click on '+ New Message' which should be underneath the name of the class on the menu. Choose one of your class mates in the drop down box beside the words 'New Message To' at the top of the page. Type your message in the box provided and click 'Send message'