This is not the latest version of this documentation, for the one that is upto date, please see the latest version (2.6.9)
By default all 5 (1 SFP port and 4 LAN Ports) are bridged to LAN (br-lan):
Network Settings - LAN - Bridge Slaves
If you'd like to use the raw device as a custom interface which usually for a SIP trunk or WAN failover, you can remove a port from the bridge by just clicking on it.