Answer:
An ip address has 2 level hierarchy: network ID and host ID. The network id identifies the network the host is connected to .The host ID identifies the network connection to the host rather than the actual host.
The host ID is assigned by the network administrator at the local site. The network ID is assigned by ISP.
In the computer, in order to know the ip address of system, use the run prompt in which ipconfig/all command will give the ip address of the system.
Answer 2:
To find out your external ip which is what is really important if you are doing port fowarding and other tasks use the site: http://www.whatismyip.com.