ALERT: Starting with GetSimple version 3.1, sitemaps will be generated automatically every time either a page or site-setting is changed. You will be able to view the sitemap via Theme → View Sitemap. From this screen you will also be able to regenerate your sitemap.
GetSimple has a built in sitemap generator. If you want to create one, or refresh the one you already have, navigate to Theme → Generate Sitemap
if you are having trouble creating your first sitemap, ensure that your server has the correct permissions (try CHMODing the root installation folder to either 0755 or 0777). If that doesn't work, create a blank file within the root of your instllation (next to gsconfig.php) with the filename of sitemap.xml. CHMOD that file to 0777, then go back and try to regenerate the sitemap using the menu link shown above.
By default, when you create a sitemap, the system pings all the major search engines. You can turn this off within gsconfig.php file by enabling the constant GSDONOTPING