Your router comes with JUNOS Software installed on it. When you power on the router, all software starts automatically. You simply need to configure the software so that the router will be ready to participate in the network.
To configure the JUNOS Software, you must specify a hierarchy of configuration statements that define the preferred software properties. You can configure all properties of the JUNOS Software, including interfaces, general routing information, routing protocols, and user access, as well as some system hardware properties. After you have created a candidate configuration, you commit the configuration to be evaluated and activated by the JUNOS Software.