This chapter shows examples of usage scenarios, including a basic login, some use and control of presence information, and instant messaging. The technical details behind these usage scenarios are discussed, providing insight into how Office Communications Server and Communicator work together to provide useful functionality. Such technical understanding is essential for administrators who need to implement, configure, and troubleshoot Office Communications Server in their enterprises. This chapter also provides the core background on basic server and client operations in terms of discovery, connectivity, and communications over the Session Initiation Protocol (SIP) and as such is useful to refer back to as reference material when exploring the other scenario chapters.