Can someone please explain what Priority is on a XML sitemap. Also what is Change Frequency & Last modification? I am seeing all of this here http://www.xml-sitemaps.com/
Complete explanations are given at AutoMapIt in the forums, but in short... Priority is how you compare one of your pages to another of your pages. Change Frequency is how often your page gets updated or changed. Last Modification is a timestamp of the last time your page was actually updated. All of those are optional, but the priority or (correct) lastmod would be the most important.
Here is an article I once wrote about sitemap priority values Looking at the date... Oh my god time flies fast
search engines want to know, how fast your site contents changes. so xml sitemap help those bots to let them know about it.
The priority, although I'm convinced is a useless item, supposedly says how important that page is compared to other pages on your site. Considering that the SE's give no relevance to it whatsoever, it's useless.