It simply turns fibre into Ethernet (and, with some ISPs/plans, to copper phone). As timmmay says, you can pretend that it doesn't exist. There is no "control panel" website or anything like that and it doesn't have an IP address.
The ones that Chorus use have no (programming) interface faceing the customer side, apart from the one that is used by the installers to set the ONT's ID. All additional programing/firmwear updates are done via the fibre interface from the equipment side. The ONT's ID must match the one in the POLT's (Exchange Equipment) tables for successful intercommunication between ONT & POLT - Thats why there is no point in taking the ONT anywhere but where it is supposed to be as it will not communicate even if it has a optical connection.