Overview
Users with a primary account are covered under the Microsoft Campus Agreement which includes Office 365 for home-use. You can access this software through http://portal.office.com. You'll sign in with your Pitt email address, then once on the Welcome page click the Apps tab on the left hand panel > Select the pull down button Install apps from the right hand side > Select Microsoft 365 apps:
Detailed instructions are available for Accessing Office 365.
Note that home-use access of this software expires if you leave the University.