The Controller is the block every Refined Storage system will need. It is the core of your system.
Connecting devices to the Controller
You are supposed to connect every device that depends on a storage network connection to the Controller.
You can connect devices by connecting Cable to them.
Cables are not always necessary, as long as the devices are next to each other in any direction a connection will be established as well.
It does not do much by itself, but it does have storage for Forge Energy so connected devices can run. It draws a fixed amount of FE/t, depending on which devices are connected to it.
If the Controller runs out of energy, it will turn all connected devices off.
When the Controller is broken, it will maintain its energy.
Multiple controllers on the same network?
Each Refined Storage system can only have a single Controller, if you attempt to connect another Controller to the same network, both or one of the Controllers will drop as items in the world.