The directory C:\Inetpub\wwwroot\wss\VirtualDirectories\80 is already being used by another IIS Web Site.  Choose a different root directory for your new Web application.

Solution:
1. Ensure you have a proper dns name / entry in the hosts file of your server for the new url you are wanting to create.
2. Ensure you have typed in the ‘host header’ typed in when creating the new web application.
3. If this doesnt work, open IIS Manager – Start>run> inetmgr> and verify the home directory – it could be located on a different drive.

Do you want to publish your SharePoint intranet or internet site to your users with a nice friendly url (or hostheader)?

This article can be also used if you want to rename your web application.

You would have to change the Alternate Access Mappings in SharePoint.

In SharePoint Central Administration, Click Operations.
In Operations, under the Global Configuration area, click Alternate access mappings

Next to Alternate Access Mapping Collection, click on the down arrow and click on ‘Change Alternate Access Mapping Collection’.

Select your Web Application

Click on Edit Public URLs

Then type in your desired URL (hostheader) in the Internet field as shown below:
For Example: http://www.mysite.com

Alternatively, you can change the Intranet fields for SharePoint intranet deployments.

Click Save and youre done!

But before you go, make sure your DNS resolves to your web server IP address. Ping and make sure that works. You could also modify your hosts file to test this out.

You have now successfully enabled SharePoint to resolve requests to your new URL.