Apple iWork '08 - Manual (Page 85)

Chapter 2 Getting Started with Numbers 85
3 In the Function Browser, select Numeric on the left and SUM on the right.
4 Click Insert.
The function appears in the Formula Editor and the Formula Bar, and contains
argument placeholders for you to replace with your own values.
You can type a function name
here to search for it.
You can also scroll through the
list to find a function.
Select All to display all the functions, or click
a category to view a subset of the functions.
A brief description of the
selected function appears here.
Click to view a help page describing the selected function.