An FLA file is a Flash source file that contains all the animation and graphics. To manage this file you should have Adobe Flash MX 6 or higher installed on your computer.
To open an FLA file in Adobe Flash editor you should select "File/Open" from the top menu and browse to the location of your FLA file. A simpler way to open your file is just to drag and drop it from your file browser to your Adobe Flash editor window. Also, if FLA files on your computer are based on the Adobe Flash software, you can just double click it in your file browser and this file will be opened and ready to use.
Note: If you see the “Missing Font Warning” alert message, it means that you have not installed all the fonts included in the package. To get more information about fonts installation read the Working with fonts section.