There are 2 methods to do it and they are:
1. URL Redirect: URL Redirect is the standard method for URL Forwarding. When the client types in your domain name they are redirected to the web server that your page is hosted on. The only drawback of this method is as the person is looking around the site the URL that is displayed by the browser is the one of the actual web page, not your domain name.
2. URL Frame: URL Frame is similar to URL Redirect except that instead of redirecting the client to your web page, the web page is displayed in a frame from our web server. With this method the client’s browser will display your domain name (for example: www.yourdomain.com) while they are using your site and not the actual URL to your page (for example: home.yourdomain.com).
This functionality is available on all domain registrars or domain hosting control panels.
To demonstrate; we have used a site (www.apps4rent.us) registered with ENOM and have used their control panel to add host records. (See the screenshot below)
We have used the 2nd method in our example.
So that you can have a look at the result; we have added an URL Frame to www.apps4rent.us. On typing www.apps4rent.us in your browser you will see the contents of home.yourdomain.com. Moreover, when you click on any link on the site; the URL remains to be www.apps4rent.us.