You can do it in the Public Website section (under Website > Settings on the left-hand-side panel).  In there, you can enable/disable your public page by turning on/off the toggle for Public Website or you can view your public page by opening the link visible in the Public Website field (next to the toggle itself).  If your page is disabled, you will see a red warning at the top of the public website when you open it (and the URL will include ?redirect=no) informing you that this page is not available to the public. The Public Website is turned off by default and you can change it anytime.