A sitemap is an index of all pages on your directory. A sitemap may assist in search engines finding pages on your site that normal indexing may not be able to locate.
1) Get your domain verified by following these instructions: How to verify my domain on Google
2) Go to your Site Manager. Then go to Promote → SEO Center. Then click on the "Click Here To Go To Sitemap Index" button.
Notice: The abovementioned instructions to access the sitemap are valid for version 13.1 and below.
From the version 13.2 on, here are the instructions to access the sitemap.
Go to your Site Manager. Then go to Promote → SEO Center → Webmaster tools:
Click on the "Click Here To Go To Sitemap Index" button.
3) Select and copy the part of the URL where it says: custom/domain_1/sitemap/index.xml
4) Go to your verified Google Search Console property and click Sitemaps from the menu on the left.
5) Paste it to where it says Add a new sitemap and click the Submit button.
Repeat this step more than once if it doesn't work out the first time. It is necessary a "Success" message to be displayed after clicking on "Submit"
If it returns a "Couldn't fetch" error just refresh the page and try again. If it returns any other error, please contact the support team via email: firstname.lastname@example.org
Notice: It is necessary to have some content on your site in order to function correctly, such as listings and categories, for example.