The resolution is the number of pixels in the horizontal and vertical directions. The higher the resolution, the more information you can see on the screen at once. Refresh rate refers to the number of times a monitor redraws the screen each second. Higher refresh rates mean less flicker on the screen and less strain on the eye.
Refresh rate is irrelevant on LCDs, which are usually optimized for a fixed resolution.
Almost all CRTs sold today can display a range of resolutions, but there is a limit to the number of pixels you can see clearly. Any monitor worth its tube will support 75Hz or higher at a given resolution. Most graphics cards are more than ready to meet these same rates, although you should check first if you're planning on running particularly high resolutions. Though 1,024x768 is the optimum resolution for most mainstream work, it's not usable on smaller displays. Also, if you buy a larger display, we recommend a slightly higher refresh rate of 85Hz, something that any new card and monitor should support up to at least 1,280x1,024.