There’s loads of online resources available for the User State Migration tool. There’s a printable walkthrough on Technet and a series of  video walk-throughs by John Baker.

TechNet Video: (Part 1 of 5) Overview of User State Migration Tool
TechNet Video: (Part 2 of 5) What’s New in the User State Migration Tool 4.0
TechNet Video: (Part 3 of 5) User State Migration Tool Scenarios
TechNet Video: (Part 4 of 5) Hard-link Migration in the USMT 4.0
TechNet Video: (Part 5 of 5) Offline User State Capture in the USMT 4.0