Apple iWork '09 - Manual (Page 22)

Although you can type a function into the text field of the Formula Editor or into the
formula bar (Numbers only), the Function Browser offers a convenient way to add a
function to a formula.
Select a function to
view information
about it.
Search for a function.
Insert the selected function.
Select a category
to view functions in
that category.
Left pane: Lists categories of functions. Select a category to view functions in that
category. Most categories represent families of related functions. The All category lists
all the functions in alphabetical order. The Recent category lists the ten functions most
recently inserted using the Function Browser.
Right pane: Lists individual functions. Select a function to view information about it
and to optionally add it to a formula.
Lower pane: Displays detailed information about the selected function.
To use the Function Browser to add a function:
1 In the Formula Editor or the formula bar (Numbers only), place the insertion point
where you want the function added.
Note: When your formula requires an operator before or after a function and you
haven’t added one, the + operator is inserted automatically. Select the + operator and
type a different operator if needed.
22 Chapter 1 Using Formulas in Tables