The nunchuck is the extra controller that you need for certain games that goes in your other hand. It attaches to the wii remote via a cable which goes from the bottom of the nunchuck into the bottom of the wii remote.

It fits nice and comfortably into the hand and isnt heavy at all so it does make your wrist ache to hold it. It has an analogue stick on the front and two buttons on the top which has different uses depending on which game you are playing.

It is not needed for all the games, but is needed in ones such as sports games in which you have to swim, run or box etc. If you dont have one attached then the wii wont let you play the games that require it.

They dont come with a wii remote when you buy one, so if you need an extra one you have to buy it seperately. This is something that I think should come as part of the package of you are buying an extra controller, but it isnt too much of an issue now as they can be bought for as cheap as £3 if you do a bit of shopping around - the internet is the best place to find one, on sites such as ebay or amazon. There are cheaper unofficial ones out there though so make sure it is an official nintendo one before your buy.

They can come in black or white, and you can also buy them wireless now too, which is beneficial as the cable that runs between the nunchuck and the wii remote can get a bit irritating, particularly if you are playing sports games which require alot of movement as the cable can swing around and get in your way, or not be long enough if your going at the quite vigorously and flinging your arms around alot.

Overall the nunchuck is good, its cheap to buy, lightweight and sits comfortable in your hands, and I have never had one go faulty on me.