Select the button in the Library panel, or else you get default buttons in the "Common Libraries" to go to common libraries go to Windows - Common Libraries





Then it will open up the common library panel, there you will find a lot of buttons, select a button and just drag and drop to your movie

Right click on the image, and select EDIT.....then it will open up the button editing area. There you will find four main Keyframes as Up, Over, Down, Hit.

In the button's Timeline, add a new layer for sound. For example say that you want your button to give a sound efect when you mouse over the button. Then in the sound layer which you created now, insert a keyframe in the second frame named "over" as shown below in the image.

Then import the sound file to the library, the sound you want to add to the button when mouse over it.

To import the sound file, go to import - browse and double click. Then it will be placed in your library panel. To open up the library panel go to windows - Library



Then in the library panel you will find the sound file.

Ok now go to Insert - New Symbol

then it will open up a small window, from there you can give a name to your sound movie. Im gonna give as "mc_btn-sound" and from the you will find they have given three options as Movie Clip, Button, and Graphics. Tick "Movie Clip" from there and press OK.

6.

Now you are in the first layer, now go to the library panel and select the sound file and drag and drop to the movie place. Then there you will find the property bar below the movie, from there you get a option called "Loop" set it to "1".





Ok now go back to the scene again, by clicking "scene". And again double click on the button, then there you will find you have added a new layer for sound, make sure it is empty




Select over state Keyframe as shown on the image, then go to your library panel from there you will find the movie clip you made for the sound effect. Mine is named "mc_btn-sound". Drag and drop it to the movie, make sure you are in the "over" frame.

Ok the sound effect is added to your button. Now press Ctrl+Enter to preview your movie...