Basically, just change your image mode to multichannel. Then add your channels in the channels palette. You pretty much won’t work in the layers at all, just the different channels.
I would recommend starting with a blank image. Add your a new channel for every ink you’ll need. Then delete any channels which don’t represent colors you’ll be using. Then double-click on the channel thumbnail to give it a useful name (ink color) and to assign the preview color for the channel – click on the color sample thumbnail bringing up the color selector, then choose custom and switch to an ink palette (like pantone).
Note this is just a preview color for display, it has no bearing on the final separation. Colors won’t be displayed accurately. For example you could assign a channel the display color light pink (which would be very light on screen) or dark green (appears dark). When you do your separation they’d both separate as grayscale.
Actually you’ll just be working in grayscale in the individual channels. If you try working in the layers the color you use might get split across multiple channels. It’s easier to have individual grayscale images for each color, just copy and paste the artwork into the color channel you need.
This site <
http://www.creativepro.com/story/feature/19805-2.html> has one of the few tutorials I’ve seen. Multichannel is a real pain if you’re working in a lot of colors. You might look into using Illustrator instead.
