A track being public means that anyone can listen to your track, and it will show up on your SoundCloud profile page and your followers’ Streams. Private tracks are exclusive, giving you control over who has access to your tracks and who doesn't. Private tracks won't show up on your public profile and can't be searched for within SoundCloud.
To change the sharing settings of your track, go to the edit page and select either Private or Public on the Basic Info page
You can change the privacy setting for multiple tracks at once through your Tracks page.
Click on the tracks you would like to change the privacy setting for, and click ‘Edit tracks’ and choose ‘Privacy and tags’ from the dropdown:
If you're on a mobile device, you can also edit your track's privacy settings on the SoundCloud Pulse app by going to the track's edit section and editing the "Make track public" section.