Question

To apply the same formula of cell to the cell below it drag down

Answer 1

Select the cell that has the formula you want to fill into adjacent cells.

Rest your cursor in the lower-right corner so that it turns into a plus sign (+), like this:

Cursor resting on fill handle

Drag the fill handle down, up, or across the cells that you want to fill. In this example, the figure here shows dragging the fill handle down:

Cursor dragging fill handle down

When you let go, the formula gets automatically filled to the other cells:

Values showing for cells that have been filled

To change how you want to fill cells, click the Auto Fill Options button  Auto Fill Options button that appears after you finish dragging, and pick the option that want.

For more information about copying formulas, see Copy and paste a formula to another cell or worksheet.

Tips:  

You can also press Ctrl+D to fill the formula down in a column. First select the cell that has the formula you want to fill, then select the cells underneath it, and then press Ctrl+D.

You can also press Ctrl+R to fill the formula to the right in a row.