When you create a repository, you can choose to make the repository public or private.
If your GitHub Enterprise Server instance is not in private mode or behind a firewall, public repositories are accessible to everyone on the internet. Otherwise, public repositories are available to everyone using your GitHub Enterprise Server instance, including outside collaborators. Private repositories are only accessible to you, people you explicitly share access with, and, for organization repositories, certain organization members.
Organization owners always have access to every repository created in an organization. For more information, see "Repository permission levels for an organization."
People with admin permissions for a repository can change an existing repository's visibility. For more information, see "Setting repository visibility."