The Unified Software Development Process, Analysis and
design is driven by use cases. Tons of books have been written about the subject (just do a quick search on Amazon), however many authors seems to "over complicate" the matter.
I've found two great articles about Use cases, which I think is worth reading if you're new to Use cases..
1) Use cases - An Introduction: usecases_intro.pdf (315.54 kb)
2) Driving Development with Use Cases: usecases.pdf (349.23 kb)
UML is, of course, also a big issue if you're beginning your quest into use case-driven software development projects. If you're new to UML take a look at What is UML?