A sitemap is a file (usually sitemap.xml or sitemaps.xml) or set of files that tell the search engines what posts make up your site. As a search engine crawls your site to be able to index and rank the data, these sitemaps come in handy for their ability to easily discover pages on your site.
Think about the fact that your site is a set of links. If there was no sitemap, then the Search Engines would try to parse you home page recursively looking for links to amass what the structure of your site looks like. By using a sitemap, you’re giving them the info in an easily consumable format. This can only help!
Typically the SEO plugins will create these and keep them up to date for you, but initially, you’ll want to submit your main sitemap to Google using their Google Search Console.
If you’ve never used Google Search Console before, it can be a treasure trove of information. Even if you have Google Analytics set up but are not getting a lot of hits, the Google Search Console can show you where you rank and how many impressions of your site occur even if the user’s aren’t choosing your link. I’ll write more about how to set yourself up with Google Search Console soon.