When you finish editing a level, you need to convert it to a format that is usable by your game platform, so that you can test its behaviors or distribute a final product. Typically, the game programming team writes a plugin that converts the level to a platform-specific game format. Alternatively, they can create a build process that converts the saved level file to an intermediate format or to the format used by the game.
For more information about writing plugins that convert a level to a format that a gaming platform can consume, see the ATF Reference (available from https://github.com/SonyWWS/ATF/tree/master/Docs).