Use the "Start Range" field to select a range to start the fill, "Whole Range" to select the entire range to fill, and the "Fill Methods" and "Fill Series" fields to change how the fill happens.

Try selecting Sheet1!A1 as the start range and Sheet1!A1:C2 as the whole range, keep fillAuto as the fill method and column as fill series. Then click the "fillAuto" button and see the sheet fill those cells.