Magento - Creating a Configurable Product (e.g. color / size attributes)

A good tutorial on Magental on Products Attributes (e.g. size / color)

It is common on Colthes / Fashion / Sport e-commerce website as you may need to setup 1 sku only.

Creating a Configurable Product
There are a few steps involved: 

1. Create the attributes that will be configurable by the user - for our example they will be Size and Color
2. Create the attribute set that will be assigned to the variant products - for our example, we’ll call it “T-shirt”
3. Create the individual variant products
4. Create the configurable product, and add the “T-shirt” attribute set
5. Add the individual variants to this configurable product

Creating Attributes
Below are screenshots of how the configurable attribute “Size” is set up.

Please check out here: http://www.magentocommerce.com/knowledge-base/entry/tutorial-creating-a-configurable-product/