The Oculus Rift is a 3D headset that puts you right into the game. You don't see your real surroundings anymore with this thing on, so you need to be able to find your equipment without looking at it.
The EDTracker is just a head tracker, similar to the TrackIR. You strap it to your head and your avatar in the game of your choice will move his head in the same direction you move yours. Since you still have to look at your screen you can set the translation for both yaw and pitch axes to make it so your virtual head moves further than your real one does, e.g. you move your head like 30° to the left and your avatar in the game moves his by 90°. This might feel strange at first but is something you should be able to get used to in no time.