You can double-click the fill handle (the dark black dot that appears in the lower right corner ) of a selected cell to fill the contents of the cell down a column for the same number of rows as the adjacent column.

For example, if you type data in cells A1:A15, type a formula or text in cell B1, press Enter, and then double-click the fill handle in cell B1, Excel fills the data down the column from cell B1 to cell B15.