The Nectar Administrator can hold up to 6 doses of Nectar, as well as regulating the base level of Nectar in the soldier's bloodstream. At the press of a button, a dose of Nectar is administered and the soldier has a temporary nectar boost. This nectar boost seems to be able to be prolonged by killing enemy targets.
All Administrators are controlled remotely, by a Nectar Administrator controller.
The base level of Nectar in the soldier's bloodstream can be adjusted on the Administrator, presumably as soldiers are exposed to Nectar more need to maintain a higher base level of Nectar in their system. This is what Teare adjusts down to allow Carpenter to start seeing more of reality. When the Nectar flow is disrupted enough, the administrator can detect this and it reboots to try and restore Nectar flow.
Damaging the Nectar administrator causes it to stop regulating the Nectar flow, causing a Nectar Overdose.