newbie: hmtl form to select items from mysql db

Hola, PHP folk! I am slowly getting a handle on what php/mysql can do. I have a mysql database that I can display in a web browswer with php. That part is working just fine, but it was the easiest part, of course. My goal is to create an order form sort of thing were a certain quantity of each item is specified, and the final step is creating the invoice with the grand total is tabulated, etc, etc. I know this is standard stuff, my immediate question is more specific. I need some direction in creating the html form where the items are selected. As it stands now, I have six digit ID numbers that identify each item. The first digit represents the general class of items and the second digit represents a sub-class. The remaining four are arbitrary. What I would like is for the user to 1)pick the class, see the available sub-classes 2)pick the subclass, see the items available 3)pick the item 4)pick quantity If anybody can point me to a tutorial or examples, I would be most appreciative. Danny