Decide what button type best suits your needs.
Basic steps for creating buttons
Most people choose button symbols for their flexibility. Button symbols contain a specialized internal timeline for button states. You can easily create visually different Up, Down, and Over states. Button symbols also change their state automatically as they react to user actions.
Movie clip button
You can use a movie clip symbol to create sophisticated button effects. Movie clip symbols can contain almost any type of content, including animation. However, movie clip symbols do not have built-in Up, Down, and Over states. You create those states yourself, using ActionScript. A disadvantage is that movie clip files are larger than button files. Use these resources to learn how to create a button with a movie clip symbol:
Tutorial: Movie Clip Buttons (ActionScript 3.0, Schoolofflash.com)
ActionScript button component
Use a button component if you require only a standard button or a toggle, and you don’t want to customize it extensively. Both ActionScript 2.0 and 3.0 button components come with built-in code that enables state changes. So, you don’t have to define the look and behavior of button states. Simply drag the component onto the Stage.
ActionScript 3.0 button components allow for some customization. You can bind the button to other components, and share and display application data. They have built-in features, such as accessibility support. Button, RadioButton, and CheckBox components are available. For details, see Use the Button component in Using Adobe ActionScript 3.0 Components. For examples of how to use Button components, see AS3 Button Component Quick Start.
ActionScript 2.0 button components are not customizable. The component enables state changes. For details, see Button component.
The area that is responsive to clicks by the user. Defining this Hit frame is optional. If your button is small, or if its graphic area is not contiguous, defining this frame can be useful.
The contents of the Hit frame are not visible on the Stage during playback.
The graphic for the Hit frame is a solid area large enough to encompass all graphic elements of the Up, Down, and Over frames.
If you don’t specify a Hit frame, the image for the Up state is used.
You can make a button that responds when a different area of the stage is clicked or rolled over (also called a disjoint rollover). Place the Hit frame graphic in a different location than the other button frame graphics.
Associate an action with the button.
To make something happen when the user selects a button, you add ActionScript code to the Timeline. Place the ActionScript code in the same frames as the buttons. The Code Snippets panel has pre-written ActionScript 3.0 code for many common button uses. See Add interactivity with code snippets.
ActionScript 2.0 is not compatible with ActionScript 3.0. If your version of Flash uses ActionScript 3.0, you can’t paste ActionScript 2.0 code into your button (and vice versa). Before you paste ActionScript from another source into your buttons, verify that the version is compatible.
Create a button with a button symbol
To make a button interactive, you place an instance of the button symbol on the Stage and assign actions to the instance. You assign the actions to the root timeline of the FLA file. Do not add actions to the timeline of the button symbol. To add actions to the button timeline, use a movie clip button instead.
Enable, edit, and test button symbols
By default, Flash Pro keeps button symbols disabled as you create them. Select and then enable a button to see it respond to mouse events. Best practice is to disable buttons as you work and enable them to quickly test their behavior.
To select a button, use the Selection tool to drag a selection rectangle around the button.
To enable or disable buttons on the Stage, choose Control > Enable Simple buttons. This command acts as a toggle between the two states.
To move a button, use the arrow keys.
To edit a button, use the Property inspector. If it isn’t visible, choose Windows > Properties.
To test the button in the authoring environment, choose Control > Enable Simple Buttons.
To test the button in Flash Player, choose Control > Test Movie [or Test Scene] > Test. This method is the only way to test movie clip buttons.
To test the button in the Library Preview panel, select the button in the Library and click Play.
TechNote: Button hotspots are active even though the buttons are covered with other objects (Adobe.com)
TechNote: Adding actions to shared buttons (Adobe.com)
Video: Troubleshooting ActionScript 2.0 button symbols (Kirupa.com)
Additional button resources
TechNote: How to create a new button (Adobe.com)
TechNote: Creating advanced buttons (Adobe.com)
TechNote: How can one button do different things at different times? (Adobe.com)