To add an external audio file (a song or voice recording) to exported videos, follow these steps:
1. Go to Settings > Video / Audio
2. Select the Audio option at the bottom of the window.
3. Click the folder icon and choose audio file. Click the trashcan icon to remove file.
4. If you want to use this audio file in all your videos, check Always Use This Audio.
Audio Files and Audio Notes
In the lower menu, check Audio Notes to disable external audio on clips which have audio notes added. With this option enabled, clips without audio notes will maintain the original soundtrack of the video. To mute original audio check Mute Registers without Notes.