If it works like Pages, in the file browsing window there should be a button on the bottom that looks like a rectangle with an arrow coming out of it. Click that and there should be an option to Export. Once you do that, the next time you sync, the file should be there in iTunes file sharing on your computer. You need to do this every time you want to access the files on your computer in iTunes sharing. There is no auto syncing of the files. Again, this is for Pages but I'm guessing Apple made it the same for all the iWork apps.