Click the “Project Info and Sharing” button in the top-left corner of the table of contents.
Check the “Publicly accessible?” box. This will make available a persistent url (“www” web address) that the public can use to view a read-only version of the project in its current state. This url can be shared and linked to. If this box is not checked, the project will not be available or visible via this url.
Click the “Save” button.
To make the project unavailable to the public again, simply uncheck the box.
If in the future you make the project publicly available again, the same url will be provided.