There are two sound effect files located in the
impact.wav for the plane’s explosion and
three_tone.wav for the ring collection sound. You can add
AudioStreamPlayer nodes to the
Ring scenes to play them at the appropriate time.
For the background music, which should be played in a loop during the game, add
AudioStreamPlayer to the
Main scene, using
Riverside Ride Short Loop.wav for Stream. Since it needs to play automatically at the start, you can check the Autoplay box.
The audio for this game is intentionally kept simple and upbeat. While there’s a sound effect for each major game event (flying through a ring, crashing), you could also try adding additional sounds for the airplane engine, bonuses, or a warning when fuel is low. Experiment to see what works for you.