Sometimes you might find a quick reminder of the formula syntax useful when working in Excel.
If this is the case then type an equal sign followed by the function name and then Ctrl+Shift+A. For Example typing =Sumif and then using the keyboard stroke Ctrl+Shift+A will give you: =Sumif(range,criteria,sum_range).
In 2010 you will find Excel even more helpful. As you begin to type your formula it will bring up a list of formulas matching your text typed so far (see image below), double click on the function you require and Excel will then display the syntax for you.
The non-bolded arguments are optional.