Your best bet is to check out the AC3D manual on the Texture Coordinate Editor (TCE). This page also has some useful info on using the TCE:
http://www.ac3d.org/ac3d/tutorials/carbody/index.html
Once you've learned how to use the TCE, the UV map exporter will probably make a lot more sense.
One of our fellow users posted a TCE tutorial, but it appears to be offline? I remember it being a well-done video --- perhaps someone still has it to share...
http://www.ac3d.org/forum/showthread.php?t=3291
Good luck,
Dennis