An RGB monitor consists of a vacuum tube with three electron guns -- one each for red, green, and blue -- at one end and the screen at the other end. The three electron guns fire electrons at the screen, which contains a phosphorous coating. When the phosphors are excited by the electron beams, they glow. Depending on which beam excites them, they glow either red, green, or blue. Ideally, the three beams should converge for each point on the screen so that each pixel is a combination of the three colors.

Also see The Science of Color and Northern vs. Southern Hemishpere Monitors in the Did You Know . . . ? section of Webopedia.

Converting RGB to CMYK
This page gives a detailed technical explanation on how to convert RGB images to the CMYK color system for printing.

RGB vs. monochrome monitors
From Vision Research Graphics, the page provides information on selecting a monitor.