You can add an attribute to a dimension either automatically or manually in Microsoft SQL Server Analysis Services.
To create an attribute automatically, on the Dimension Structure tab of Dimension Designer in SQL Server Data Tools (SSDT), select the column that you want to map to an attribute, and then drag that column from the Data Source View pane to the Attributes pane. This creates an attribute that is mapped to the column, and assigns the same name to the attribute as the name of the column. If an attribute that uses that name already exists, Analysis Services adds an ordinal number suffix, starting with "1" for the first duplicate name.
To create an attribute manually, set the Attributes pane to grid view. In the name column of the last row in the grid, click the <new attribute> item. Type a name for the new attribute. This creates an attribute that is not mapped to a column and that has default settings for all its properties. You can set the mapping in the Properties window of SQL Server Data Tools by configuring the KeyColumns property for the new attribute.