XML-Sitemap is one of the very basic things that a SEO should do while doing on-page optimization. If we use non-technical terms, XML is a way to tell search engine, how many pages your web site have and which page is more important and which is less important. This is a standard and all search engines understand.
There are many online free and paid tools which can help you in making XML site map and this is suggested that you put this sitemap in root of your website and name it as “sitemap.xml”.Each entry of Site map have a <loc> tag which contains Url , a <lastmod> tag which contains date at which it was last modified in YYYY-MM-DD format , a <changefreq> which contains frequency of changing of webpage a,d a <priority> tag which tells how much important a page is .Valid range for this is 0.1 to 1.0 but giving high priority to all page will not help you . All these four tags are inside <url> tag and one </url> tag makes a entry . One More tag <urlset xmlns="http://www.sitemaps.org/ schemas/sitemap/0.9"> is Present in each Xml sitemap.
After putting this Xml site map in root of your website submit it from your Google and Bing webmaster too. It will help your site to be crawled properly and thoroughly by search engine boat.