As described in Select modules, a teacher can enable or disable Manhattan modules by clicking on the Configuration button on the classroom's Main Menu, then selecting the first item in the list:
Go here to turn modules on and off. You can also change the course information that appears on various screens throughout the system.
You'll note there's just one checkbox for the People module:
Enable this module
As you'll see, the People module is different from other Manhattan modules in that you won't find any messages here. Instead the People module allows students to see each other's "personal info pages".