What should I set for the host value in the A/AAAA records?

The custom domain tutorial: How to do Custom Domains with Fly · Fly
says:

  • Head over to your DNS provider and add A and AAAA records for example.com with the IPv4 and IPv6 values.

What should I use for the host value?
Nevermind: I see it’s @.

It says to add a CNAME record:

CNAME _acme-challenge.mydomain.com => mydomain.com.jzoy0.flydns.net.

I assume the first value goes in the host field & the 2nd value goes in well … value?