1) make a selection of the area you want to be a spot
2) on the channels fly-out menu, choose "new spot channel"
3) enter pantone # & solidity
4) save as a photoshop DCS 2.0
sometimes if you are doing complicated traps there can be issues with the metallic ink and other ink types, so you may want to discuss art with pre-press before sending your files in, as you may need to modify your design.