Selling socks in four different sizes and colors? A book that has a hardback, paperback, and deluxe edition? Then you'll want to note this variance so your customers can select which version of the product they'd like to buy.
To add different types, sizes, or colors to a single product listing, go to your product’s page. Under Multiple Options, click on Add Options.

Here you can specify the options that are available to customers interested in this particular product.

These options can be anything that fits your product choices. Here we’ll use Color and Height. And then provide the choices available for each.
To finish, select an Input Type for each option, so the customer can select the color and height they want for this product. You can choose from dropdown list, multiple choice and color choice.
If you choose color choice, you’ll need to assign a color for each option choice by clicking the small color box to the left of each color name.

Once you’re finished, hit save. Now you have a long list of what are called Product SKUs. These SKUs are nothing more than a breakdown of every possible combination of choices a customer is able to make with the Options we provided them for this product.
This level of detail is provided so that you can vary the price and weight for each combination when and if it's appropriate to do so.
The most useful option available to the individual SKUs is the ability to associate different images with each one by clicking the small image icon to the far right as you scroll over them.
The most useful option available to the individual SKUs is the ability to associate different images with each one by clicking the small image icon to the far right as you scroll over them.

Once this is all finished, your customers are shown a very clean interface from which to make their choices.