While ranking better in Google is rather a complex process, we will focus now on the sitemaps and discuss the other procedures later.

A sitemap is a method of informing the web crawlers about the pages of your website. It is an XML file with a list of all links in your website.
The sitemap xml also contains info about how often the information is changed and how important the page is.

While the Sitemap is a recommended procedure for making your website easier to be discovered, the modern web crawlers index your website starting from the homepage and following all links.