The Actions panel (Windows>Development Panels>Actions) lets you choose and type in Actionscripting.

In Flash the name of the Actions panel appears as either:
Actions-Frame
Actions-Button
Actions-Movie Clip

This is a wonderful indicator of what you have selected on the stage (button or Movie Clip) or in the timeline (frame actions). Always double check this. It helps you to understand what you are about to program and what you have selected (even experts make selection mistakes).

Select from the actions on the left in the Actions panel to add actions to your Script pane.

Actions Panel Options

On the top left of the panel, you will find:

-a search icon: to find script text
-a replace icon: to replace script text
-a targeting icon: to help you find Movie Clip & Button objects to target
-a check icon: to check syntax
-a code formatter: cleans up the justification of the code for easier reading
-a show code hints icon: very useful for hinting on code possibilities when you might forget them.

On the top right of the panel, you will find:

-an icon for the actionscript help dictionary: so useful
-view options

From the top right pull down arrow you will find

-print: prints your script
-export: exports your script files as text files
-import: imports script files
-many options easily found on the panel itself listed above

On the bottom of the panel

-pinning scripts: to save them. Note: this keeps you from putting in a new script.
-an area to the bottom left that shows you where you are in your file