Adding options to your product is very simple. Let's take our sport socks and try to sell them in different sizes.
I hate to say this but to have this working you may need to use a decent browser like FireFox or Google Chrome, IE may throw an error saying "Not Implemented". Although this is standard html...
Next, click the "Add option" to add an option to the product. You can add as many options as you like.
Save your product (again) and that's it! Now you can sell your socks in different sizes.