To reuse a section in another course, in the navigation bar on the left choose Existing sections.
NOTE: In this case the section is shared, which means that if you delete any content/questions from the shared section, these items will be removed from all courses containing this section as well. Please keep this in mind when you delete something from shared sections.
Drag and drop sections you want to reuse to the corresponding column. Click Done when ready.
The reused section is marked by a special indicator. If you click on it you will see where exactly the section is reused.
If you want to delete a section, click on the "More options" (three-dot ellipsis) button and choose Delete section.
You can delete a shared section from all courses or only from the current course.