I am very new to all this and I would like to create a sitemap using Google's Sitemap Generator but I can't even open the initial file once I've downloaded the folder. I am working on a MacBook Pro and I have Python installed and Omni Outliner (not sure if that's relevant) - don't know where I'm going wrong. I find it all a bit mind boggling! Can anyone help me with the basics?
Working with the Sitemap Generator suggested by Google is very difficult. I would suggest you to try some GUI based Sitemap Generators. There are many free online and offline sitemap generators. You can use GSiteCrawler, its free and higly configurable. Or else there are many websites providing the service for free.
However, if he using a Mac OS his choices are probably somewhat limited when it comes to desktop programs. You could try a few running them through a Windows emulator... But I have zero experience with Mac so... I do not know if that is a feasible route to go