Experiments are private by default.  You can make an experiment public if you have full access rights to that experiment (usually the case for experiments you have uploaded).

Click on the experiment you want to make public from the experiment inbox.  The experiment summary page will appear.
Look for the section called "Sharing Permissions."  Click on the button called "Share with Everyone."

This will make your experiment available to everyone.  Users will be able to view any saved illustrations, download files and clone the experiment.  Note that working illustrations will not be available to users.