1. Click on the cell where you want to enter the formula.
2. Type the formula using the dollar sign to lock the constant cell. For example, if your constant cell is H7 and you want to multiply it by cell A1, the formula would be =A1*$H$7.
3. Press Enter to calculate the result in the cell.
4. Copy the formula down the column by selecting the cell with the formula and dragging the fill handle (the small square in the bottom right corner of the cell) down to the last cell in the column that you want to apply the formula to.
5. The constant cell reference ($H$7) will stay the same in all the formulas, while the cell references for the other cells will change based on their relative position to the formula.

That's it! Now you have multiplied many cells by a constant cell and locked the constant cell in the formula so that it stays the same when you copy it down the column.