Architecture & Views (You can skip this part on the first reading)
Use Case View
UML is for visualizing, specifying, constructing, and documenting with emphasis on system architectures (things in the system and relationships among the things) from five different views
Architecture - set of significant decisions regarding:
Organization of a software system.
Selection of structural elements & interfaces from which a system is composed.
Behavior or collaboration of elements.
Composition of structural and behavioral elements.
Architectural style guiding the system.