Each computer on the Internet is assigned a unique numerical address, called its IP address. Each packet moving around the Internet contains the IP addresses of the sender computer and the destination computer. Using the IP addresses, the routers move the packets across the Internet until they reach their destination machines.
Where does your IP address come from? When an organization connects to the Internet, it gets a set of IP addresses from the Internet authority. Your Internet service provider or system administrator will assign your machine an IP address. If you are using a PPP/SLIP account, your PPP/SLIP provider will assign your computer an IP address.