If you want to total a set of numbers you would use the Autosum (sum function) in Excel. This enables you once clicked to drag over the numbers in question and it will add them all up. A shortcut way of adding the sum function in is to select the cell where you want to have your answer and on the keyboard press:
ALT and =
This will then put the sum function in that cell and you can then drag over your numbers. So you no longer need to bother the mouse to do this!