Well you understand the primary function. Each of the channels lets you independently edit the colours of that channel. If you have a RGB image then the channels you have are Red, Green and Blue. If, however the image is HSV or CMYK, then you will have the appropriate channels. One thing to keep in mind is that all channels in the GIMP are 128 bit greyscale.
The next major function of channels in GIMP is for transparency (namely the Alpha channel). If you want an image with transparency (like png) you can add an alpha channel that masks the image, allowing the pixels to be opaque, transparent, or somewhere in between.
The last function of channels is storing selections. You can take any selection (including feathering) and save it as a channel. You can then edit this channel as if it were a greyscale image, including painting, erasing, and all the associated effects (blur, scrip-fu, etc). This lets you "save" different selections that you can "load" as selections later.
Hope that helps. If you have any other questions (or are looking for use examples), just ask!