The first step is to be sure you understand what Use Cases and State Models are all about. This is not rocket science, however, and can be completed in short order.
Use Cases: Read “Use Cases: Requirements
in Context”, ISBN 0-201-65767-8
State Models : Read Chapter 21 and 24 of
“The Unified Modeling Language User Guide”, ISBN 0-201-57168-4
Obtain USP Training – Not required, but you might want to jump start your project with a mentor approach. See Titus Corporation