Add a new site to track in Google Analytics

Click Admin in the top menu

Account -> Property -> view

if it's a new subdomain of a domain you already track

Or for a whole new domain:

When adding the new view, it will default the name to "All Website Data" but instead name it after your exact subdomain.

May also want to add it in 'Google Search Console' (formerly 'Google Webmaster Tools')

//TODO: add site in Google Search Console

See also