Hi,
Which chunk of code are you using, there is quite a lot on that page. You should start at the top with simple and work your way down.
So start with this AGV_test_turn2.pde, the waypoints are documented in there as floats flat2 flon2 etc. Play with that code until you understand it. Then work way through the rest. The best thing to do is get the steering working, with out having the motors connected, or with the bot on a support so the wheels are off the ground.
You should be able to create your own waypoints with a hand held GPS, so you know exactly where they are in relationship to your bot. You will need to do that to make sure the steering turns the correct way.