In Magento, Attributes are quantifiable or descriptive aspects of a product, from the color, to the manufacturer, to the SKU number. There are two kinds of attributes in Magento: Simple Attributes and System Attributes. By default, Magento includes all the necessary System Attributes. These cannot be deleted, and every product must have each of these attributes. Therefore, all Attribute Sets must include these attributes. For example, if you were to create an attribute for color, with values of blue, green, yellow, etc., you may want to apply this attribute to an Attribute Set for shirts, which you sell in various colors, but you probably would not include it in an Attribute Set for DVDs, for which color is not really an applicable attribute
More info about Attributes in Magento, you can find in this link http://www.magentocommerce.com/wiki/welcome_to_the_magento_user_s_guide/chapter_3#attributes
1. ADD A NEW ATTRIBUTE
To create a Simple Attribute, navigate to Catalog > Attributes > Manage Attributes, and click Add New Attribute in the top right of the page
After creating new attribute, you need to add it into an attribute set which you use for your product.
In our theme, there are 3 built-in attributes: Featured Products, Hot Products, Special Deal. These attributes are used for EM Filter Products Widget.
2. ATTRIBUTES SET
An attribute set is a collection of attributes. For example, if you to create an attribute for color, with values of blue, green, yellow, etc., you may want to apply this attribute to an Attribute Set for shirts, which you sell in various colors, but you probably would not include it in an Attribute Set for DVDs, for which color is not really an applicable attribute. To manage attribute sets, navigate to Catalog > Attributes > Manage Attribute Sets, you can create new or edit exists attribute set.
After making any changes in the attributes and Attribute Sets, you may need to reindex the data in your Magento and flush the cache.