About installation options for GitHub Apps
When setting up a GitHub App, you can choose to have the installation flow be either public or private.
Note: GitHub Apps are only compatible with the REST API v3 at this time.
Public installation flow
Public installation flows have a landing page where users begin the installation flow. This link is provided in the "Public link" field when setting up your GitHub App. For more information, see "Registering GitHub Apps."
Private installation flow
Private installation flows allow only the owner of a GitHub App to install it. Limited information about the GitHub App will still exist on a public page, but the Install button will only be available to organization administrators or the user account if the GitHub App is owned by an individual account. Private, or internal, GitHub Apps can only be installed on the user or organization account of the owner.