<select onChange=" "> ??

Hi,

I'm trying to understand how the onChange command in a select tag works.

What I wanna do is to choose a person in a select, when selected it updates
the next select with years that this person has info on when year is selected
a 3rd select is updated with the months the person have info for in that year.

When you select the month it will display the info for that month in that year
for that person.

everything is stored in a access database.

Anyone who can explain how this works in an easy way?
Maybe someone have a link to info about this?

/Speedy