If you want to point a domain that you have to a different domain name or subdomain, one way to do that would be to use a CNAME record. By setting up such a record, the domain being forwarded loses all its records (A, MX, and so on) and instead, it takes the A record of the domain address it is directed to. This way, if you are using a web design service by some company that gives you a subdomain, you can use an actual domain and not only will it be forwarded to the site that you have set up, but it will also be displayed in the web browser address bar at all times. Alternative possible uses of a CNAME record are to redirect all the targeted traffic from various subdomains to their main domain name, or to use the webmail service of your webhosting company by using webmail.your-doman.com, for instance. The latter will work only by setting up a CNAME record for a subdomain simply because such a record created for the main domain address makes it impossible to use e-mail addresses.
