A sitemap should be the definitive 'list' or 'index' of all the pages on your website.
The sitemap.xml file is a standard file that is used to tell the search engines all the pages on your site. XML is a file format (like .csv) that provides data in column format.
Why is this important?
Google, and other search engines look to index your site by following links in your site and from external websites. The sitemap is a trusted 'map' followed by search engines that should guide them to every page on the site. Without a sitemap, Google is relying on your site to provide a link to every page on the site.
Without a sitemap you run the risk of 'hiding' pages from Google's index.
The main search engines, including Google, Bing and Yandex offer free 'Webmaster' accounts that will tell you facts about your site, including a count of how many pages they have indexed on your site. They use your sitemap.xml to benchmark the pages indexed on your site. Without the sitemap, you won't have a benchmark of site performance.
How can I create a sitemap?
There are a number of free tools that can help you create a sitemap. Wordpress users have access to a few different tools that will create and publish your sitemap. Take a look at this one, or the bundled tools inAll in One Webmasters or Yoast SEO plugin. You can also use free online tools like https://www.xml-sitemaps.com to create your sitemap. You will then need a techie to upload it to the site.
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