Discover Photoshop Channels

You can view the channels individually by selecting them such as you would in the layers palette. You can use the channels palette to make lots of corrections to an image and work with it 'under the hood' (such as finding a channel that looks the worst and adjusting just that channel to improve the image). As a basic Photoshop user you just need to understand what they represent for now.

You can view channels together by viewing two of them at the same time.

It's important to note that I am in RGB in this image so it is the Red Green and Blue channels that you are seeing.

Under the Image menu you can change the actual color mode of the image without breaking a sweat. Try changing an RGB to a CMYK. 

CMYK stands for cyan, magenta, yellow and blacK. It is the printing press default color mode worldwide. These four color channels are what you see used in magazines and flyers.  In the channels palette you will now see the different color channels which makeup the CMYK mode.

You can also change the image to Grayscale which creates just one channel. Be careful when doing this to Save As: to create a copy or go back in history to your original state if you're just testing this out.

Go back to Image: Mode; and switch back to RGB.  RGB is the standard color mode used for home printing and web use.