When a user receives a new Message, they will see a red bell icon over the upper-right Tool Icon:

Click on Messages to view new messages.

The Messages window will appear.

When a check appears in the New column, that message has not been seen yet. This only shows the first time the Messages window is opened.

The Commands column contains icons to work with the task.

• Click the trash can icon to delete the message. Note that if the task is not addressed, it will appear the following weekend.
• Click the wrench icon to address the issue. Collaboration will navigate to the associated page and prompt the user with an action. If the action is performed, the message will automatically be deleted. For example, when clicking on the wrench for a missing document, the user will be prompted to create the new doc. If they click Yes, the New Document form will be displayed and upon saving, the message will be deleted.
  If not completed, the user may return to the Messages window at a later time.

If you want to send messages please see the article on collaboration