I'd suggest starting with a decent book on color management, or at least a good chapter on the subject. You need to get up to speed on a bunch of basic concepts to comprehend what is going on. Very briefly, Prophoto RGB is a very wide gamut RGB space within which any real world color (and a lot of physically impractical color gamut) will fit. It's sort of an imaginary space far bigger than any physical device has the capacity to display. Your monitor is an additive color device with its own gamut, often limited to something close to sRGB for inexpensive monitors, or approaching the wider Adobe RGB for an expensive one; the image you see is by nature different from the reflective color seen in a print. A really good inkjet printer on semigloss/luster paper can reproduce a gamut approaching that of Adobe RGB in most directions, sometimes exceeding it in a few areas.
A good way to visualize different profile gamuts is on screen using a software tool that produces a three-dimensional and rotatable gamut plot, and that permits you to compare two different profiles. For example, my monitor profile plot is much, much "wider" than my printer profile along certain axes; but the printer has a rather "deeper" gamut in other directions. At least I can conceptualize how they differ, though real-world appearance of the print is the true test. I confess that I'm using Microsoft's free and relatively brain-dead color management applet, but...did I mention that it's free?
I believe Bill Atkinson wrote an entire suite of color management and profiling applications himself, to assist in the iterative process of developing profiles for the extremely non-linear Epson 7600/9600 inkjet printers. At least that's what I recall from the one-day course in inkjet printing and Photoshopping he gave at George Eastman house about 3 years ago.