Just to add a little more info:
The "good" bacteria aka ammonia/nitrite eating bacteria aka nitrifying bacteria live on surfaces, not in the water itself (although they will float around in it for a short while when they go to find a place to live). Thats why adding water from someone else's tank won't help cycle your tank, but taking gravel or filter media or decorations will.
The BioWheels are folded paper basically, but because they are are folded, there's more surface area and more bacteria can live there (think apartment building vs a ranch home). Plus, the good bacteria need oxygen, and since the BioWheels spin in the tank and air, the bacteria on there get more oxygen and the colony grows even larger.