Click the cell in which you want the formula to appear.
In the Formula bar, type =sum(C3:C12) (which translates to "add the values in cells C3 through C12") and press Enter.
The values in the specified cells are added together.
INTRODUCTION
There might be times when you don't want to use AutoSum because you want to perform calculations on specific cell references. In these instances, you can simply type the desired formula directly into the cell. You can include any cells in your formula; they do not have to be next to each other. Also, you can combine mathematic operations for example, C3+C4 D5. After you enter a formula, if you change the values in the referenced cells, Excel automatically recalculates the value of the formula based on your changes.
TIP
Canceling a Formula
If you start to enter a formula and then decide you don't want to use it, you can cancel it by pressing the Esc key.
