Volume: Around 0.05 is okay.
Spatial Blend: If it's 2D, you can hear the same volume throughout your whole game no matter where you are. If it's 3D then it depends on how far you are from the object.
Doppler Level: As you are walking/running, if you have this turned on, the sound will have a dopple(water-like) effect which does not sound right. So turn this off by setting it to 0.
You can tell as you walk closer to the speaker it starts to sound louder!
For a background music for the world overall, we just need an Audio source on the Hierarchy itself.