i had a problem designing this web form,

the form contain COUNTRY, STATE, LGA, and the form object are drop down menus/list.
i want the user to choose the country and it will generate the values of the state from the database,
when the user choose the state it will generate the LGA from the database tool,

how do i do it?

i use php mysql for my application

you will need ajax for that or you use javascript onchange event.
the difference > Ajax ( no reloading of page) while javascript (there will be a reload of page)

using javascript
1. define a funtion that load that same page and pass the value of the list in the url
2. call the funtion onchange of list value
3. write a php code to load values of the country, state and LGA base on that.

the code,

Not to put sand in your food tech pros but you don't necessarily have to use ajax, though it would be ideal.

He could also call a function that refreshes the page each time a selection is made. I only mention this as ajax usually has a huge learning curve (I know it was for me) and so sometimes, starting with the basics makes sense. Alternatively, he could use a ready-made framework like scriptaculous, jquery or mootools that already has done the dirty work for him. Of course, having the page refresh 3 times, for each selection, especially on a slow connection isn't exactly what one would call ideal but sometimes, tis best to crawl (page refresh) b4 u walk (ajax).

Again, not putting sand in your garri. Just offering another alterntive.

*Strolled by* oh well, many ways to solve the problem.
@poster, i have some ajax scripts that seem to solve that
problem. Buuut, if you do not know javascript/ajax, then i
will never advise you to use that approach, as you will
surely get stuck.

so if i want to use jquery how do i use jquery to achieve that

There are plenty of tutorials at jquery.com - just search for the right plug-in, thatz all. I haven't used it myself but I know it is there. with libs like jquery, the good thing is, you just download the necessary files, modify to suit your needs and you are up and running in no time.

Good luck!

Exactly, jquery will be better and faster too.