NetworkTables is the underlying networking technology to send and receive values between the robot and the SmartDashboard and LabVIEW dashboard. It can also be used by your own programs to distribute values between the robot and clients, for example, vision processing or custom dashboards. In this example:
http://wpilib.screenstepslive.com/s/...client-pc-side
you can see how to write a robot-side and client-side (PC) program that reads and writes some values to NetworkTables.
Brad