Changing your DNS changes where your services are hosted from and is a top level change. There are many components within the DNS Zone file that allow you to specifically modify where this information goes individually. These are the A, CNAME, MX Records respectively.
The A record lets your DNS know what Server IP you are trying to pull your site from.
CNAME records are for setting up the server to instead point to a website address such as www.domain.com
instead of a server IP and this is referred to as the Common Name.
MX record is for your Email services and tells where to try to access your mail server from.
Whether you modify the DNS or one of the other attributes really comes down to what you want to be pointing where.