login to magento
click on catalog >google sitemap
click on “Add Sitemap” in the top right hand corner
give the file a name e.g. sitemap.xml
add a file path or just /
select which store view you would like to make a site map for.
save the sitemap.
once it has saved the click on the Generate button on the right.
you can the test your sitemap by adding /sitemap.xml to the end of your URL and you can add this to your Google web master account.