Niloy,
Adding sound to Flash is really very easy. You can use any .mp3 or .wav file in Flash. Usually we choose to use shorter sounds for flash because it saves time to load the flash files. To use as a background music you should use loops. flashkit.com has a very good collection of free loops for you to download. To use with buttons or various other effects you should collect some fancy fx sounds. Again flashkit.com. These sounds are usually like 5-20 kb in size.
Once you chose your sound you have to now import it from the File-Import. Once imported, you can see it in the library. If the library panel is not open, open it from Window-Library. Now decide in which frame you want the sound to play. Drag the sound icon from library panel to that frame. It's that easy. Once you get this working, you can ask me more specific questions. There are many kool things yu can and should do with sounds in Flash.
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