Hope this helps a little:
Listen 80 is the most common or Listen Your IP address:80
The Listen directive instructs Apache to listen to only specific IP addresses or ports; by default it responds to requests on all IP interfaces. Listen is now a required directive. If it is not in the config file, the server will fail to start. This is a change from previous versions of Apache.
The Listen directive tells the server to accept incoming requests on the specified port or address-and-port combination. If only a port number is specified, the server listens to the given port on all interfaces. If an IP address is given as well as a port, the server will listen on the given port and interface.
Multiple Listen directives may be used to specify a number of addresses and ports to listen to. The server will respond to requests from any of the listed addresses and ports.
For example, to make the server accept connections on both port 80 and port 8000, use:
Listen 80
Listen 8000
To make the server accept connections on two specified interfaces and port numbers, use
Listen 192.170.2.1:80
Listen 192.170.2.5:8000
IPv6 addresses must be surrounded in square brackets, as in the following example:
Listen [fe80::a00:20ff:fea7:ccea]:80
If you use Listen 80, then for servername: try your site name:80
Example
www.don'tknow.com:80
The ServerName directive sets the hostname and port that the server uses to identify itself. This is used when creating redirection URLs. For example, if the name of the machine hosting the web server is simple.example.com, but the machine also has the DNS alias
www.example.com and you wish the web server to be so identified, the following directive should be used:
ServerName
www.example.com:80
If no ServerName is specified, then the server attempts to deduce the hostname by performing a reverse lookup on the IP address. If no port is specified in the ServerName, then the server will use the port from the incoming request. For optimal reliability and predictability, you should specify an explicit hostname and port using the ServerName directive.
If you are using name-based virtual hosts, the ServerName inside a <VirtualHost> section specifies what hostname must appear in the request's Host: header to match this virtual host.