Double-click a field in the table to select it as part of the result. It will appear in the lower Selection window.
It defines an alias for the column, to rename the column in the result.
It define an aggregate function. Following options are available:
MIN: Minimum, and
If you select an aggregate function, an Alias must be defined.
Check the following example, that counts the number of description languages of each material.
On the right side you have the options to move up, move down or delete the fields.