There is a couple of different types of ambient sounds you can use to create effects in a video game.
You can use music as ambient sound to add mood. Fast pace music can make a section of a game fast pace while dramatic music can make another scene sad. Most games use music to set the mood. Music can be found in games as non-diegetic sound (sound that is not coming from a visible source). But games like Grand Theft Auto have diegtic sound (sound coming from a visible source).
Ambient sound does not have to be music though. You can get natural sounds as well, you can get wind and other similar natural sounds to set moods as well. Horror games have hardly any music as ambient sound. They create a mood by having no music to create suspense and the sound of wind or any other similar ambient sound creates a scary feel. Alien Isolation uses the same sound techniques to create the same feel to create the suspense of the alien is near and could attack at any time.