I believe, at least for windows, it has been dummified for us. all those ICM files? those are colour profiles.
[colour profiles and printing/viewing etc]
in ps, (I use 7) try running the colour manager and try out the sRGB, Adobe98, your monitor.ICM and your printer.ICM etc (use "custom/advanced" if cannot see all the ICMs)
if normal JPG, changing to printer.icm will usually fade it out, cos ur ink behaves diff from the monitor.
go get an Adobe98 file from dpreview's galleries and view it in sRGB then Adobe98 u'll see some parts smooth out nicely... meaning sRGB has a smaller set of colours...
ok now that u've seen some diff types. how to switch between?
go to Edit or somewhere (see version) and look for adjust->change(or assign) colour profile. here u can convert ur e.g. Adobe98 file to BJC1998.ICM then u'll print out looking like the image on screen. (of cos black is always a bit crappy).
since RGB as prev mentioned is addi(c)tive, while CYMK is reversed. therefore some super bright n pretty colours on monitor cannot be achieved by ink unless it's wax/metal(special)-dye etc.
so using CYMK, or converting to CYMK just before u print, is to preview if some of the pretty colours in your work might not be achievable printed.
test, by doing a gradient using the rainbow palette, then convert to CYMK from RGB. see that ur colours start to look duller or muddier, that's it exactly. and turning on gamut warning is supposed to blink areas of colour that TOTALLY cannot be printed proper.
this is also a reason why slides look nicer than prints, cos the colours have a glowing (radiating? forgot the term) medium vs the reflective paper of a print.
sounds messy? pls ask portions then maybe I can (mis)guide u further..