CMYK Working Spaces in Photoshop

CMYK working spaces are a little more involved than RGB options, listed in the preceding section. They serve a threefold purpose:

-->CMYK is the color space to which Photoshop converts your RGB file when you choose Image➪Mode➪CMYK.

-->CMYK is the color space you will view your RGB image in when you choose View➪Proof Setup➪Working CMYK (see the upcoming section on soft proofing colors).

-->The CMYK color space determines how a CMYK file is displayed on an RGB monitor.
There are specific color profiles for printing in Europe, Japan, and the United States. Those four CMYK options are divided between those for coated and uncoated paper, and sheet-fed or Web printing presses. The latter two have different percentages of ink coverage and paper stock. I would leave the setting at U.S. Web Coated (SWOP)v2 unless your commercial printer tells you otherwise.