2 drop down menu with php and mysql

Hi,
I am new in PHP, I need your help to resolve my problems

1- I used mySql and have two tables, one for categories and the other for articles. One categorie may have many articles.
I need 2 drop down menu (categorie and article) in which the data will be retrieved in the database.
The items in the drop down menu of articles will be changed when I click in one categorie associated.

2- How I can add one or many items from articles drop down menu to one area text (by add button) and remove item from this (by delete button)

Thanks for all your help
Mr_Bonds