Manage only a subdomain with Google Cloud DNS

I own a domain example.com and I am happy with where its DNS is hosted. I do want to delegate to Google Cloud DNS only a new subdomain bar.example.com.

1. Is this possible?
2. Could you point me to example code?
3. What I need to do to the DNS settings of the servers hosting example.com.

You should just be able to create NS records in example.com called bar and enter the nameservers (one per entry) they gave you. That's called a "zone cut" and anybody looking up, say, baz.bar.example.com will be told by example.com to check with Cloud DNS (the same way com told them to check with example.com). When they ask Cloud DNS, they'll get the answer.

So -

1. Set up the zone bar.example.com on Google Cloud DNS
2. Add NS records at example.com listing the Cloud DNS nameservers given
3. ... that's it! Try it out.