Use of the special keys
As stated previously, the special keys are the ten function keys, the Del key, the Help key, the cursor (arrow) keys and the Esc key.
Cursor Keys
Cursor keys are a convenient way to control the movement of the cursor inside an application. Here are some standard ways to use them:
Unmodified Cursor
Move a small amount in the specified direction. Often this is one unit such as a character in a word processor or a pixel in a paint package, but it could be several pixels in an application where navigation is more important than fine control.
Shift + Cursor
Move to the appropriate extreme of the window, or shift the view by one windowful if you're already at that extreme.
In applications such as a word processor where the two directions are not symmetrical, shifted cursor keys could take on different meanings. Shifted up and down cursors would page through windowfuls while the shifted left and right cursors would show more on the left and right if there is more to show. Of course it is often the case that the width of the document fits in the window, so the shifted left and right cursors could act as beginning- and end-of-line commands (or edge of window if the cursor isn't constrained to the form of the text).
Alt-Cursor
This is used for application-specific functions. It's usually semantic units such as words in a text processor or fields in a spreadsheet.
Ctrl-Cursor
Move to the appropriate extreme of the project (beginning, end, extreme left, extreme right).
In the word processor example, the up and down cursor keys would take the cursor to the beginning and end of the file, respectively. But again, if the file fits within the width of the window, the left and right cursor keys combined with Alt would act like their shifted cousins.
Function Keys
Function keys should generally be reserved for the user to define. If your application does make use of them, then it should at least allow the user to redefine or modify them.
Help Key
If your application has built-in help, use the Help key to trigger it from the keyboard. Avoid giving the user that helpless feeling he gets when he presses the Help key and nothing happens.