Posting a track as public means anyone can listen to your track, and it will show up on your SoundCloud profile page and your followers’ plays. Private tracks are available only to you, they won't show up on your public profile and can't be searched for within SoundCloud.

A ‘scheduled’ track (only available to Artist Pro users) will remain private until the date which you have specified in the settings after which it will go public. 
 
 

Individual tracks

To change the sharing settings of your track, go to the edit page and select either Private, Public or Schedule on the Basic Info page:

Multiple tracks

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 then tap the small pen icon:

You can add the same genre, tags and edit the Advanced settings for the selected tracks:

If you're on a mobile device, you can also edit your track's privacy settings on the SoundCloud app by going to the track's edit section and editing the "Make track public" section.