Here are some tutorials for using the A* Pathfinding System:
Firstly, make sure you have read the Get Started Guide in the docs
A* Pathfinding for RTS or Tower Defense Style Games
quill18 has created an excellent tutorial for getting started with the A* Pathfinding Project. It explains a lot of stuff the above get started tutorial does not cover, so check it out: http://youtu.be/bkCLqPpopvE
This is one of the most up to date youtube tutorials (as of May 2013).
Using the A* Pathfinding Project with AI Behaviors
AI Behaviors package in the forums:
Make A 2D Game With Unity3D Using Only Free Tools
The tutorial uses a quite old version of the A* Pathfinding Project, but it is still relevant even if not everything will match up with the current version of the system.
Tutorial in Chinese