Webmail
Use this to connect to Outlook Web Access (OWA), also known as Webmail, to access your e-mail without the need for special software. This can be used on any computer, including public ones.
Microsoft Office 365 Portal
Use this to change your e-mail password. This can be used on any computer, including public ones. Once you change your e-mail password, you will need to enter the new password into the "Sign In" application on all of the computers you use. You will also need to enter the new password into mobile devices (iPhone, BlackBerry, etc.).
Microsoft Online Services Sign-in Assistant
Use this to install the Sign-in Assistant software before using Exchange Online for the first time. This software periodically notifies you when your password is within 14 days of expiration.