We are a group of high school students working on a Capstone project to detect cars in parking spots. We are planning to use the XBee Wireless transmitters (as seen Microcontroller | Microcontroller Projects - Maker Shed)
We have never programmed an Arduino before, and were wondering if anyone had any tips for us, or if anyone has any experience working with XBee and the Arduino combined.
Thanks!
You did not search well enough otherwise you would have found this 
and order a copy of this book, it will tell you all!
To learn to program the arduino , best spend a few days in the tutorial section to see how the programming language works.