A function is a mathematical calculation which returns a single value. Excel includes a function button in the standard toolbar - fx - to provide easy access to these. They are grouped into categories from which you can see the wide range of uses a spreadsheet has. You will find a working knowledge of spreadsheets has become essential to a wide range of professions.
The most commonly used function is the SUM function and it appears in the Excel standard tool bar as ‘AutoSum’. The symbol used is the Greek letter Σ (sigma or capital S) which is standard mathematical notation for 'sum of'. To obtain the sum of a column of numbers you select the cell underneath the numbers, click the 'Σ' button, check the range of cells included in the sum and then press the Enter key.
In this case you could double click the Σ button and the function would choose the cells immediately above as those to be summed. In some other situations you should not double click the Σ button because the range of cells to be summed may not be those immediately above.
The AUTOSUM function works in exactly the same way for a row of numbers.
Note the form of the SUM function: =SUM(A1:A3) and =SUM(A1:C1). You could type these directly into the cell instead of using the Σ button.
Other functions on the SUM button include AVERAGE, COUNT, MIN and MAX. You should be able to work out fairly quickly what each of these extra functions do:
AVERAGE(range) - finds the average of the numbers in the range
COUNT(range) - finds the count of the numbers in the range
MIN(range) - finds the smallest of the numbers in the range
MAX(range) - finds the largest of the numbers in the range
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