Use-case diagrams present a high-level view of system usage as viewed from an outsider's (actor's) perspective. These diagrams show the functionality of a system or a class and how the system interacts with the outside world. Use-case diagrams can be used during analysis to capture the system requirements and to understand how the system should work. During the design phase, use-case diagrams specify the behavior of the system as implemented. 

Rose automatically creates a Main use-case diagram in the use-case view. There are typically many use-case diagrams in a single model.