Channels indicate the actual frequency that a wifi device is using, This is not really Knoppix or even Linux related, you can study wifi a bit more to understands it. There are a number of channels (differs by country) but they overlap significantly, so there isn't really as much space as it might seem. Knowing what channels are in use in your location may help you set up a new router or access point on a less crowded frequency, but it is not critical for the average user to understand channels to use wifi.