1. Click on the down arrow
in the top right of the app and select Settings
2. Turn Show Local Files
3. You can turn off any of the default local file sources or click on Add Source to add a custom folder where you have music stored.
The music files of these folders will be imported into Spotify and you will be able to find them in the Playlist section of Your Library .
From there you can add them to playlists or play them directly.