i received this computer from my school due to my previous one not working, and there is no iMessage application. how do i get it? It is up to date on software and everything
MacBook Air, OS X Yosemite (10.10.3)
In OSx the application is called Messages, not iMessage It is part of the OS, and can neither be uninstalled nor installed independently. If your School gave you this computer its possible they restricted Messages via the Parental controls in OSx and you would need to request they enable it again for you if you don't have the Administrator password .
Otherwise you can try going into System Preferences->Parental Controls->Your User->Limit Applications->Other Apps->And Make sure Messages is checked.
how to install iMessage if the application is not on my computer
