Yammer is a social media tool for internal communication and collaboration within organizations. It functions similarly to Facebook and Twitter but is restricted to members with a umich.edu email address. The document provides an overview of how to sign up for and begin using a Yammer account, including creating a profile, following colleagues, posting updates, and direct messaging. It emphasizes interacting with colleagues and exploring other features like groups. Guidelines note Yammer should be used professionally and its content is not private or managed by the university.