Open YouTube and find the video with the music you want
Copy the video link (URL)
Use a reputable third-party YouTube-to-audio downloader website or app
Paste the copied URL into the downloader
Select the output format (MP3 or M4A)
Choose the audio quality (if available)
Click Download
Wait for the download to complete
Open the downloaded file in your downloads folder or media app
If prompted, allow any required permissions (mobile/desktop)