To Customize the User field as a Description Field

After defining a new field, you can customize the field either as a Lookup Field or Description Field.

Click the Description Fields tab.
Click the Add Description Field button.
In the Column field select the new User field from the drop down list.
Define a value for the new field.
Note: A User field may be defined either as a Description Field, or Lookup Field, but not both.

Note: Click Here for additional information on defining custom Description Fields.