Add a track
Switch to Timeline view.
Click Add music on the empty music row (or click an existing track to change it).
In the Music panel's Browse tab, search by keyword or filter by Genre and Vocals (all music / vocals / instrumental).
Preview a track by playing it, then click Select to place it on the timeline.
Adjust it
With a track selected, the Music panel shows:
Music Volume (0–100%)
Fade in & out toggle
These mix alongside your voiceover and any per-shot animation audio, each with its own independent volume.
Want to use your own track instead of the library? See Upload your own custom audio.