There are many ways to copy data from one cell to the cell directly below:
1) Use the copy and paste commands from the Clipboard group of the Home menu
2) Use keyboard shortcuts: Ctrl + C, move down one cell, then Ctrl + P
3) Drag the cell contents down using the fill handle in the lower right corner of the cell
One other way, and maybe the quickest, is to click below the cell you want to copy, then use the keyboard short cut Ctrl + ‘ (apostrophe) and hit Enter.
Just one more proof that Excel gives you many ways to accomplish the same task. Use that which is most comfortable for you!