The Nether Star Reactor is a type of Energy Generator.

Nether Star Reactors can be crafted in an Enhanced Crafting Table.

A Nether Star Reactor must be placed in range of an Energy Regulator, Energy Connector or an Energy Capacitor (in a straight line, not diagonals) and provided with the appropriate fuel. It is also required to be surrounded by water next to the reactor. Below and above are not necessary. It also needs to be supplied with Nether Ice Coolant Cells to prevent it from exploding.

You can manually use a reactor but in order to use cargo to automate the reactor, it requires a Reactor Access Port to be placed 3 blocks above the reactor.

The Nether Star Reactor also causes nearby Entities to get Withered.