hmm yea. i just don't know what exactly is the commander feature.. what does it allow you to do?
Let me explain it to you for a camera that does have commander mode built in: when you buy a Nikon flash (except for the smallest one, the SB-400), you get a stand which is basically a hotshoe on a piece of plastic. You can position that flash anywhere in the room you'd like (as long as there is a way for the light to hit the flash, you cannot place it behind a wall) to suit your creative lighting ideas.
Then you can ask your built-in flash to act as a trigger for the other flash: if you take a picture, the built-in flash tells the other flash what to do, e. g. how much light it is supposed to give off or if the camera should determine this automatically.
Basically it's a cheap and
very versatile way to trigger several flashes off camera. You can have up to three groups of flashes, etc. etc.
Your camera cannot act as a commander unit, so you only need to get one of the larger flashes if you plan on getting another flash to use the commander feature with. Then the flash on your camera's hotshoe acts as a commander for the off camera flash(es).