It's a relatively simple concept, the shortest explanation is the channel is the actual frequency. So for a standard wireless router using the 2.4GHz band, channel 1 is 2.412GHz, 2 is 2.417GHz, etc. Each channel is 5MHz apart but you get interference if you are use 2 channels that are close together (need 25MHz between channels to prevent it).
In the interest of keeping it simple, don't worry about the other bands available for wifi (i.e. 3.6GHz and 5GHz). The concept is the same.
If you aren't having any trouble with your network you are probably ok, but sometimes people's cordless phones or microwaves interfere with the default channel on a router (most routers come set for channel 6) and you need to change it to not lose the signal when the phone, microwave, etc is in use.