Waypoint with a GPS and compass

I want to mangle this code a bit to match it with my robot---but the problem is that I'm unsure what some of the things do!

can you help explain?

Here's the website I got the code from--I've begun to alter it but it doesn't work when I upload the code.

http://letsmakerobots.com/node/19554

The real platform for his car is further down on the page

Driving_in_the_yard.ino (14 KB)