In the data source explorer, you can copy a table by dragging-and-dropping the table onto the table container. The Apply columns dialogue box is the second window of the Copy table dialogue box.
Lists the available data fields that you can include in the copied table. To copy a data field, click its name, and then click the > button. To copy all of the fields, click the >> button.
Lists the fields that you want to include in the copied table.
Adds or removes the selected field (> or < button) or all of the fields (<< or >> button).