If an Administrator has enabled the new UI, a user will be able to enable the new UI for his/her user account (1).
While the new UI is active, the sidebar will be available on the left on all pages that the Administrator can visit and can be retracted or expanded. To view the sidebar as a different type of user, check here: Instructor and Learner.
The sidebar can be expanded/retracted from the top-left corner (1).