A sitemap lists URLs that a site wants crawlers to consider.
Why this matters
XML sitemaps are especially useful on larger sites and for content that is difficult to reach through navigation. They supplement normal internal links; they do not guarantee indexing. URLs in a sitemap should generally be canonical, publicly accessible and relevant.
Example and interpretation
An online store can include current category and product URLs without including duplicate search-filter URLs. A blog should update its sitemap when articles are published, moved or removed.
What to do next
Open your sitemap and spot-check a dozen entries. Confirm they return the expected page, have appropriate canonical tags and are linked from useful hub pages where practical.
Check a website with PageRanker to explore its observable SEO signals. PageRanker provides independent estimates, not Google PageRank.