The third section is the course components. However this is not a mandatory section and this section may also not be visible to the instructors if the website has no groups and forums enabled.
Here we can add course forum and course group:
=> Course Group: Connect a group, if creating a new course it is recommended that you create a new group for the course. By default the group created is a private group only accessible to students taking the course.
=> Course Forum: Connect a forum, if creating a new course it is recommended that you connect the group forum for the course.This will create a private group forum for the above group only accessible to students taking the course and in the group.