After you have decided on your portal site structure, you can implement it by creating the root sites necessary to support your individual namespaces. Each root site created on your portal infrastructure requires a unique TCP/IP port. The first site you create will use port 80; because that is what port browsers expect to use, you do not need any further customization so that users can type a friendly URL. For any additional sites, you need to do a domain name server (DNS) entry to support the namespace and friendly name.
For each of your root sites, follow these steps:
Open SharePoint Central Administration and select the Application Management tab.
Click Create or extend Web application in the SharePoint Web Application Management page.
Click Create a new IIS web site and change the port setting to 80 if it is not already in use so that users will not have to specify the port number in the URL. Port 80 is the standard port expected by Web browsers. If you are creating additional top-level sites and port 80 is already taken, enter a port that is not in use or let SharePoint pick one for you.
Select the NTLM or Negotiate (Kerberos) as the appropriate authentication provider in the security configuration section. NTLM is recommended for ease of configuration, but if you choose Kerberos, it must be supported by your environment. (Kerberos has performance benefits in large farm environments.)
Click Create new application ...