Monitor

Monitors obviously display what is going on in your computer. They can run at various resolutions and refresh rates. 640x480 is the default resolution for the Windows operating systems (this is a low resolution where objects appear large and blocky). 640x480 just means that 640 pixels are fit across the top of your monitor and 480 up and down. Most users prefer higher resolutions such as 800x600 or 1024x768 all the way up to 1600x1200 (and higher for graphics professionals). The higher resolutions make objects smaller, but clearer (because more pixels are fit in the screen). You can fit more objects on a screen when it is in a higher resolution. Larger monitors are better for running at the higher resolutions. If you run a high resolution on a small monitor, the text may be hard to read because of its small size, despite the clarity.

The refresh rate is how fast the monitor can refresh (redraw) the images on the screen. The faster it can do this, the smoother your picture will be and the less "flicker" you will see.
The monitor has a lot to do with the quality of the picture produced by your video card, but it doesn't actuall "produce" the graphics - the video card does all this processing. But, if your video card is producing a bright detailed picture and your monitor is dim and blurry, the picture will come out the same way