Fill downward  
This tool copies all values / formulas, from one row, going down... Until it finds the first empty cell in the cell below to the left.
Let us take a look at the example:
Consider the following scenario:
The selected range will be copied up to Row N, since the following row is empty; and therefore it marks the limit of the range to be copied.
At the first click, the column will be copied, up to the area flanked by the empty space (notice the X).
At the second click, all formats will be copied