Junos OS Configuration Basics
Usually, your Juniper Networks device comes with Junos OS installed on it, unless you specifically order it without the operating system. When Junos OS is pre-installed, you simply power on the device and all software starts automatically. You just need to configure the device so it will be ready to participate in the network.
To configure the Junos OS, you must specify a hierarchy of configuration statements which define the preferred software properties. You can configure all properties of the Junos OS, 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 Junos OS.