On most linux computer, network interfaces (e.g. the network card that you plug an ethernet cable into or a wireless access card) are configured in a mostly automatic way. In other words, as soon as you plug in a cable, the network interface is activated and just works. Or, you click on a wireless access point that is in a drop down menu and indicate that you want to connect to it.
Behind the scenes DHCP is at work, ensuring that your interface gets a unique IP address.