Beginner on rails! customize store. "Agile web development"

hey all! Uhm, dumb topic perhaps, my bad. Anyway, ive read the "How to create a shop" in the book "agile web development". But no i'd like to add some options to the product in the store, so the future customers can choose ie. a bike, and then select color and size of that bike. Iv'e given this function ALOT of taught but haven't been able to figure it out by myself, can anyone around here please help me?

How would you do it in raw HTML? Get a book on that (you can probably augment it with

I always Google for HTML html select option

When I wonder about select boxes. MS's HTML documentation is all in one site (or three), with no popup adds or other nonsense.