Learn about Sitemaps here: https://www.sitemaps.org/protocol.html#xmlTagDefinitions
This plugin will install 2 new attributes under the SEO settings for your pages.
If you want to change the default settings that Concrete5 uses on all pages, go to the Structured Sitemap Settings page and change the default settings. Any page that does not have the above attributes set will default to these settings.
If you uninstall the plugin, settings will revert to default of 0.5 priority and weekly changefreq.