An attribute is useless if it doesn't belong to an attribute set. When creating products you do not individually choose attributes that you need. The very first step when creating a product is always to tell Magento which attribute set you want to use. As already mentioned, you cannot change the attribute set of your product later on. To be able to use our freshly-created attribute, we need to add it to a set. Yes, of course, it is possible to use one attribute set only and just add all attributes to that one. But that won't be smart, because it would mean that suddenly for my TV the heel height could become a mandatory field. And it would even be shown to our visitors! No, that's not the way to do it, you need to create an attribute sets per product group, for items using the same attributes.

Navigate to Catalog | Attributes | Manage Attribute Sets to check what's already available:

Nothing much, right? Just one default set. If you installed the Magento demo content, you'll have additional sets predefined. These sets are more than what you need and in that case, you might even need to clean them up before setting up your own.