The below steps demonstrate how you can make an Active Page publicly available, where the user does not need to log in in order to browse the page:
Go to the Setup Home page.
On the left, go to Security > Security Roles.
Click on the Guest role.
Click on the Active Pages/Classes tab and click the Edit button.
In the Active Pages sub-tab, add the Active Page you wish to make publicly accessible to the right column. If applicable, do the same with the corresponding Active Class.
Click Save.