First, click on the Assigned courses tab on the left hand side. Then click Import Lesson.
You will be re-directed to a new page where you can add your own content including text, audio, translations, and more.
Once you have filled in the required information, scroll down to the bottom of the page and click Save or Save and Open.
That's it! You can verify that your lesson has been imported into your Group by going back to the Assigned courses tab in the Groups section.