Google is making it easier for office workers to start Hangouts session at work with its new plugin. The Hangouts plugin is designed to let you start or join Hangouts sessions directly in Microsoft Outlook’s mail or calendar functionality. The condition is you would need to have a Google Apps account.
You will need to download and install the Hangouts Plugin. After installing you will then see an icon that lets you schedule a new Hangout or join an existing one. You can find out more information here.
Source: Android Central