Yammer is described as the company's internal social network for secure communication and collaboration. It allows employees to find answers to questions faster by tapping into coworkers' knowledge, brainstorm ideas, and stay informed on company direction. The document provides instructions on setting up a Yammer account, including completing a profile, managing notifications, and customizing the experience by joining groups, following topics and coworkers of interest. Various ways to use Yammer features like sharing updates, files, praise for coworkers, and asking questions are outlined.