Normally when I want to point a subdomain to another domain I would just do
subdomain.example.com 14400 IN newdomain.com
However, If I want to point a full domain do I need to make two records like this?
example.com 14400 IN newdomain.com
www.example.com 14400 IN newdomain.com
All adding a cname does is point the dns entry to look up here instead - makes changing / managing multiple things that point at the same server easier. You will still need to configure webservers and what not to accept the domain.
You will need to create both records for the new domain yes, but I believe, “standards” suggest that your example.com entry cannot be a cname in its own right (it does work, but its not recommended).