In this example, the normal map of Cornelius (The same Texture for Normal and Warp mapping) was used as normal map as well as warp texture in channel 1. The checkerboard texture is used in channel 2.
you can have 10 channels for an object and map them to different things (alpha, emit, color etc)
if you are coming from a 2d image background (Gimp or Photoshop) they are very similar to layers in these 2d programs but not the same (they can be effected by the channel above but can be totally independent too)
layers in Blender are where you store your objects visibility (20 layers - those 20 square buttons in the 3D view header)
you can toggle the visabily of a layer just like a 2d image program and you will see whats on that layer
you can also have objects on more than one layer (you might put your camera and lights on all layers or maybe just one)