Once logged in (accounts are free), search what you'd like (jazz, punk, piano, etc).
Then in the left column - > select TRACKS -> then FILTER RESULTS -> then TO LISTEN then TO USE COMMERCIALLY.
Be aware that not all tracks are available for download.
VERY IMPORTANT:
Check under COPYRIGHT PERMISSION and look for CREATIVE COMMONS LICENSE. This means you can legally use the track in your own creations.
https://soundcloud.com