The handle is the small square box in the bottom right corner. When your curser is over the handle it will change to a small + sign.
Click on the AutoFill handle, and then drag to the right, left, up or down and the list will fill in automatically.
In order to COPY instead of filling a series, as illustrated on the left with “August,” hold down the Ctrl key while dragging the fill handle.
Or you can right click on pull the handle down where you will have the option to fill in the series.
Creating Custom list