Spatial Audio is audio that changes when you move your head in VR to mimic sounds that are coming from the environment. For instance, if someone speaks to your left, the sound will hit your left ear first and your right ear slightly later and with less volume. After positioning tracks in X/Y space on your equirectangular, your playback will replicate those sounds in space.
To create spatial audio, you will need to work with a DAW such as Protools HD or Reaper as well as a spatializer plugin such as FB 360 Workstation or Dear VR.
YouTube supports two different spatial audio formats:
First Order Ambisonics
W, Y, Z, X as a 4-channel audio track in your uploaded file, sample rate: 48 kHz
First Order Ambisonics with Head-Locked Stereo
W, Y, Z, X, L, R as a 6-channel audio track in your uploaded file, sample rate: 48 kHz
Please view this tutorial for a step by step on creating spatial audio for YouTube: