We create archive page for our readers so that they find our all post in a page. Similarly we have to create XML sitemap for Search Engine bots so that they find all URLs of the posts in a single page and can index it quickly.
You can check our sitemap here: http://roadtoblogging.com/sitemap.xml
So you saw that all of my blog post URLs are on sitemap page. Whenever I will write a new blog post, it will be added automatically to sitemap. Then search engine bots will crawl and index my page quickly.
According to Wikipedia,
An XML Sitemap is a structured format that a user doesn’t need to see, but it tells the search engine about the pages in your site, their relative importance to each other, and how often they are updated.
Now the question is how to create a sitemap for your blog. As you are on WordPress Platform you should not worried. Like everything we will do it using WordPress Plugin.
There are several plugins like All in One SEO plugin and WordPress SEO by Yoast by which you can create sitemap. But I prefer using Google XML Sitemaps Plugin as it is made only to generate XML sitemap. I’ve been using this plugin for 1 years and it work great for me.