Attributes are the properties a particular object.  They can be things like linetype and color, which are editable feature attributes, or things like the number of features in a file which is a read-only attribute.
Attributes can be viewed through the Status Window, the Features Window or the Points Window.  There are three broad classifications of attributes and they are as follows:
Attributes are grouped together in categories.  Many categories are pre-defined, but you can create your own attribute definitions by adding a new category using the Attributes Setup dialog.  An example of a pre-defined category is Format.  The Format category contains feature attributes such as linetype, color, and hatch.  These attributes are not read-only, so you can modify them in the Features Window.