Hi, Rahman.
Sites basically serve as a configuration template that you use for both devices that are newly discovered in Extreme Management Center and devices that are already in Extreme Management Center. While the documentation focuses on newly discovered devices because that is how we recommend you on-board your devices, you can also move a device already included in the default /World site to a new site via the
Default Site field on the Device tab of the Configure Device window. This overwrites all of the device information with the configuration you define in the new site.
While you don't need to create sites for all of your devices, we strongly recommend it as it helps keep devices with identical configurations together, allows Extreme Management Center to automatically configure new devices for you when you add them to an existing site, and allows you to update all of the devices in a site at the same time by updating the site's configuration, instead of each device individually.
For more information on where to find the field, see https://emc.extremenetworks.com/content/oneview/docs/network/devices/docs/l_ov_at_configure_device.html.
Thanks,
John