Excel is such a useful program but many people using it only scratch the surface. One of the most useful things about Excel are its functions for doing calculations. They are basically built in formula to work out everything from adding up a row or column to calculating loan or mortgage repayments. There are many scientific, engineering, financial and other functions too. One you get the hang of a few you will see how they work.
You can also use functions to look up text or values and return information. You can also cleverly combine functions known as nesting. Check out the combining HLOOKUP and VLOOKUP tutorial.
Aside from doing calculations they can display the current date or even extract text from part of a string of characters.
Here is a page of Excel tutorials I have created that have a number of functions including getting started with functions in both Windows and a Mac. I’m adding more to it regularly http://www.jargonfreehelp.com/excel-functions/