For using Winrunner you should have idea about any of the programming languages. Programming language used in Winrunner is TSL which is similar to C.
If you want to develop the scripts you should have the knowledge of TSL. But it is quite easy to learn if you can spend some time on it.
Remember that the use of any software automation tool should go through the standard software development process (requirements, design, code, and test). I hope you performed some kind of a trade off on selecting an automation tool.
At what level are you planning to test (Unit, function, board level)? Can you automate any of your previous tests?
When starting out with TSL, I actually found the tutorial to be a good place to start. Spend an hour or so working through that, then pick your favorite application and start writing TSL to drive it.
To minimize your confusion, I'd recommend using a Windows standard application like Notepad to write your "learning" scripts against - it's reasonably stable and present on every Win32 computer that you'll come across. Once you've gotten a feel for how TSL works, then try writing scripts for your PCB application.