You can create a new attribute in a dimension by using drag-and-drop editing in the Dimension Designer.
To create a new attribute automatically
In Dimension Designer, open the dimension in which you want to create the attribute.
On the Dimension Structure tab, in the Data Source View pane, in the table to which you want to bind the attribute, select the column, and then drag the column to the Attributes pane.
Analysis Services creates the new attribute that has the same name as the column to which it is bound. If there are multiple attributes that use the same column, Analysis Services appends a number to the attribute name.