Here are some links to resources to get you started adding audio assets and music to your game.

Music
Here are some places to get music from:

Sound Effects
Epic Sounds has a good guides on how to use sound in video games. Their list of how to create foley effects is useful too.

  • Room tone audio can make your game locations feel more real.
  • Boom Library has collections of high quality sounds for sale.
  • FreeSound, which has – you guessed it – free sounds.

Audio Software

Troy of Darc Productions helped me find some of the above sources.