a question on channels

what are they and what do they do? I'm not new to photoshop, i just want to increase my understanding

They can do quite a bit! For new users, they can be an abstract concept, I'm still learning more about them myself. I guess the main use of channels is to perserve selections you've made in a current project. You then can "reload" the selection from the channel you saved it in. This is cool.

When you use the render>lighting effects filter, you can load a channel and get different lighting effects depending on what you have done to that channel. For example, you can make a selection, save it as a channel, apply numerous guassian blurs to it and then, in the lighting effects properties, load it and make some cool lighting effects and textures.

Those are just 2 uses, I"m sure there's TONS! I hope a lot of people respond to this with more, I'd like to know more myself...

Alpha Chanels can also be converted to distorsion map...

They are slo used on some Page layout software (like Quark and Indesign) for transparency.

Another thing you should be aware about Alpha Chanels is than some file format dont support them (like .bmp) so you may have to delete them before saving in those format...