Create or open your Facebook post.
Click the Photo/Video button (if you’re posting a video) or start composing your post.
For a video post: select the video you want to upload.
Click Music or the music note option (if available).
Search for a song or browse suggested tracks.
Select the track and choose the part of the song (if prompted).
Adjust volume or trim the audio (if options appear).
Add a caption, then click Post (or Share).
For a Reel (if available to you): create a Reel and tap Music to select a track, then publish.
If Music isn’t shown: update the Facebook app, try again, or post from a different device/format (Music availability can vary by region and account type).