You might get some of that info from one of this videos in the VID section.
Basically, it's a matter of copying what you need (a layer or a selection) from Layers (into a new channel). Select area in layers, I like to have that element onto it's own layer so that I can select every pixel of that one area. Then Command/Control Click on Layer to make a selection of every pixel. If you are using the magic want or color range to make a selection, (while it's still selected, showing the marching ants), you can move over to the new channel and fill with black...or paste. If you copy from layers, it's copying as if it were a greyscale. So Copying yellow, will paste grey. Typically, you want your richest yellow areas to be solid in channels. So, you might need to do this in both ways. Copy/paste, and Select using color range/wand and then move to channels and fill with black.
Create a new channel, (small page icon at bottom right of window) and then paste into that by having that channel selected (activated) and then paste.
ScreenExpress seems to be doing the same thing but via the Menu bar at top under Selections I think.
Double click on your channel to assign it 's type.
NAME, PMS 123
SPOT,
COLOR, choose color that it will show...Click COLOR and then COLOR LIBRARIES. Choose a pantone color from the list...or, you can create a custom spot color name like Russell Dark Grey.
SOLIDITY. This is simply a ink density representation (on screen). Doesn't affect the output but helps you make choices visually when crating the seps. (e.g) a 110 base white may be 100% solidity while a 230 base may be 60% solidity. Then colors over top with a solidity of 20-50% will show a little of the shirt color coming thru that color...where that color goes off the base.
Now, to print from Accurip.
Type Command P or Control P
Under PRINTER, Choose your Accurip Printer model. You may see your printers name...and another one (if Accurip was set up to recognize your printer correctly) you will see another printer with the name accurip next to it.
Under COLOR HANDLING:
Make sure your Photoshop print settings are set to (Separations). This will enable you to print to Accurip with a file that has nothing in it but the channel seps and Accurip will see them.