Just plug in the compaq monitor into your tell's blue vga out port in the back or side of the laptop. Then you will need to tell your laptop to use the screen. Normally you can do something similar to holding the "fn" key and hiting f8. Pressing it multiple times should togle between only your laptop screen, to both your laptop screen and your monitor, and finally just your monitor.
On most laptops there is an FN key around where the ctrl+alt keys are. Its blue and when held down and used in combination with another button it does things. For example, on my thinkpad fn+pg up turns the keyboard light on