TYPE-IN METHOD

We want to add the three numbers in cells C6, C7 and C8. To use this method type-in (using the keys on the keyboard) the following formula in cell C9:
= C6 + C7 + C8
Your spreadsheet should look like the image to the right as you are typing in this equation. Note: you don’t have to use capital (upper case) letters – we only did this because they are easier to “see” in the tutorial.
Now – tap the Enter key. Then, click on cell C9 again. The total of these cells will now appear in C9.
When you have completed typing your equation, you will see this formula in the area below the menu bar.
Change the number in cell C6 to 500 (and tap Enter). See how the total AUTOMATICALLY recalculates!!!

THIS IS THE TRUE POWER OF THE SPEADSHEET !!!
Whenever a number is entered in a cell the entire spreadsheet will automatically recalculate.
Something happened here. Notice: you typed an (equal sign) = before the cell location. If you had typed in C6 + C7 + C8, Excel would have thought this entry was a word (text) and this entry would have shown as you typed it.
Try this if you want. Any time you “create” an error in Excel, you can simply re-type or edit the formula to correct the error.
The Type in Method is really easy if you have a few numbers and can see their cell locations on the screen. If you have a lot of cells in the formula, which are on several screens, this is not such a great method. The next method will work a lot better for numbers “all over the place.”
Subtraction, Multiplication, and Division
You can type a (minus) ‑ for subtraction, (asterisk) * for multiplication, and (slash) / for division. As you become more skilled we'll, build some effective formulas – using these features.
Point Method
Move to cell C9 again and click-on it. We'll now add the numbers a second way. Tap the Delete key on the keyboard to delete the current formula.
First, tap the = and then POINT (move) the cursor over cell C6 and tap the LEFT mouse button on cell C6 (you will see a marquee box go around the cell). Now tap a + and move cursor to C7, tap the left mouse button, and tap another + and move the cursor to C8 and tap the left mouse button (notice how as you " + and point " the addition formula is being built in cell C9), now tap Enter. The same formula can be built using the arrow movement keys on the keyboard (except that you don’t have to click each cell as the cell is marked - when you move with the arrow keys). Notice, as you are entering the cell addresses, that as you place another + in the formula, that the cursor “returns” to cell C9. Also notice, as you point to each cell that it is highlighted by a “marquee box.” This “tells” you what cell you’ve pointed to. Pretty neat!
This method is good when you need to move to numbers that are spread out all over the place. Some people like it best and use it all the time ‑‑ it's your choice.