 A prime example of a spreadsheet is when prices of something are compared over time ;

 Fruit Quarter1 Quarter2 Quarter3 Quarter4 Apples £0.24 £0.22 £0.19 £0.28 Bananas £0.28 £0.21 £0.12 £0.31

But this just looks like a table - I can display a table in Word, or another package. What makes Excel different, is that it's very easy to add a total column ;

 Fruit Quarter 1 Quarter 1 Quarter 1 Quarter 1 Total Apples £0.24 £0.22 £0.19 £0.28 =SUM(B2:E2) Bananas £0.28 £0.21 £0.12 £0.31 =SUM(B3:E3) Total =SUM(B2:B3) =SUM(C2:C3) =SUM(D2:D3) =SUM(E2:E3) =SUM(F2:F3)

The above shows the text that should be entered in the "cells" in Excel in order to make them into formulas, which will be converted to the full result as soon as Enter is pressed. So where do the B2 and E2 parts fit in ? The example shown here has the formula results  evaluated. The important thing is that the column and row headings for each cell are shown here, in the same way that you would see them in Excel. Each cell is referred to by their combination of row and column headings. So the cell reference for the cell containing "Apples" is A2.

When we want to add the totals for quarter 1, we say we want the results of the sum of cells B2 and B3. If we want the total for Apples, then we want the totals of cells B2, C2, D2, and E2, or everything from cells B2 to E2. Excel lets you write the sum in either way. As long as the text is prefixed by = then Excel will know that it's a formula, and should work it out for you.
A simpler way for us to enter the function is to place the cursor in the cell where you want to place the function, and click on the button. Excel looks to see what data is located around that cell, and automatically puts the reference in for you. Of course, you can edit the cell references and choose to add more or less as you need.

So here I've just got a few values to sum, and I could have calculated these values in my head. If I was talking about hundreds of different types of fruit, and talking about every week in a year, then this would save me a lot more time. I could also add to this over time, I could use a different formula instead of SUM. For example, I could type AVERAGE instead. How many other types of formula could I use instead of SUM or AVERAGE ? Hundreds.