Functions can be used in formulas to perform simple or complex calculations. You can create a formula with a function that obtains its argument from the result of other functions. A function that is used as an argument is called a nested function. A formula can contain up to 64 levels of nesting. Note that Microsoft Excel versions earlier than Excel 2007 support only 7 levels of nesting, so you can get #VALUE! errors if you save a worksheet with more than 7 levels of nesting in .XLS format.
This document lists the Spreadsheet functions grouped by categories.