Attributes in Concrete CMS are a great way to store extra information about things like Pages and Files. For instance, you can store your Meta Description against a page - that's a "Page Attribute". You can store a "Title" against a file, that's also an attribute. You can create your own custom attributes to store against any type of data object in Concrete. You can even create Attributes to store against users, like text attributes for "First Name" and "Last Name". These come in very handy when creating themes that need to know extra information about what they're displaying, among many other things. 

You can learn more about creating and using Attributes in concrete in these Editor's Guide pages: