GitHub Learning Lab requires you to install it. Installing Learning Lab on a repository allows Learning Lab to monitor events that occur in that repository. Installing also gives Learning Lab the ability to administer that repository for the purposes of taking or authoring a course.
If you are authoring courses for an organization, you'll need to install Learning Lab on the organization. If you'd like all members of an organization to take private courses owned by that organization, you'll also need to install Learning Lab on the organization.