To easily create a sitemap for your website you can use the built-in Sitemap Generator Tool.  To configure, go to the Configure Site > Sitemap Settings tab. 

On this page you can select the sitemap file name.  Choose what gets included in the sitemap: webpages, item pages, member pages, custom pages, articles, classifieds, blog posts, and forum posts.  Choose whether to include modified date on sitemap.

You can automatically run sitemap generator tool each day and/or run it manually from your Admin Panel, on the Sitemap Settings page using the provided link.  To setup your server to run the Sitemap Generator Tool automatically each day, just follow the server cron jobs setup instructions here.