Go the following website to verify your site - https://www.google.com/webmasters/tools/home

If you select add property, then put in <<YOUR SITE URL>> it will take you to a screen to verify that you own the domain.

If you select the alternative methods tab, then select the Domain name provider radio button, it will ask you to select a provider. If you select other it will give you a TXT record that will need to be added to the DNS. If you give this to your system administrator you will then be able to verify the domain of your site.

Once verified you will then need to add the sitemap. Your sitemap URL is something like this : https://YOUR SITE URL/sitemap.xml

For more information on sitemap setup guidelines, go here -https://support.google.com/webmasters/answer/183668?hl=en&ref_topic=4581190#addsitemap