The resolution of a monitor or computer screen is expressed in pixels. Almost every non-widescreen monitor has a 3x4 height to width ratio and normal numbers are 640x480, 800x600, 1024x768 and 1280x1024. That is your screen resolution.
The '72 dpi' figure has nothing to do with this but for that I would suggest reading more about it on the website behind this link:
http://www.scantips.com/no72dpi.html They explain it a lot better than I would be able to.