AV channels are your channels where you input a signal through either scart, s-video, or those 3 cables (red,white,yellow is it called composite?)
As in they are the channels where you cannot have nomal TV reception. Modern Tv's have about 3 or 4 AV channels, usually 2 or 3 scart sockets around the back and an s-video/composite AV around the front.
Your remote should have an AV button on it... keep pressing it to cycle through the AV channels...