It takes time for all of the zone name servers located all over the world to update their lists. So, when you make a change to your Name Servers, these changes must be updated to all zone name servers around the world before your domain displays the correct web page.
This is what people mean by waiting for their domain to resolve, since the Zone Name Servers will, at first, contain your old name server settings until they update. Depending on the Central Registry (Verisign, etc.), they may update within five minutes or (very rarely) take a whole day to update.
You can use an IP Lookup Tool to determine if your name server settings have been propagated.
Google Public DNS is a Domain Name System (DNS) service offered by Google. It functions as a Recursive Name Server providing domain name resolution for any host on the Internet. - wikipedia 
Google Cloud DNS is a scalable, reliable and managed authoritative Domain Name System (DNS) service running on the same infrastructure as Google - cloud.google.com
# See also