Permalinks and SEO
Headway Videos has a simple explanation of what a permalink is and how to control WP settings for best SEO effectiveness. When you are setting up a new WP site this one of the first settings you should change. If you start your site and then change your URLs later, search engines will have potentially indexed ugly, non-user friendly, non-SEO links to your pages and then have to figure out what you changed. So get it right from the start with this nice video.
Headway seems to be gone for now, so here is an alternative source.
It is quite an old post but it still meaningful today.