Go to office.com and choose Sign In.
You will be prompted to sign in with an email. Use the Social Sciences account. This will always be @ss.ucla.edu.
The account name is usually contained in your departmental email. Your DTA can also find the account via Active Directory for your department.
The sign in will take you through the fs.ss.ucla.edu single sign-on page (if you have not yet enrolled, that can be done at: o365.ss.ucla.edu).
Once logged in, there will be a landing page. In the upper right corner, locate the Install Office button. Choose O365 Apps from the drop down.
This will install the full O365 suite of software.
Once installed, launch any program, you will find a option to sign in and proceed with the @ss.ucla.edu email once more. This will log you in across all Office programs.