Step 1: Click the 'Edit' button on the course you want to duplicate or mirror your lesson into.
Step 2: Select the 'Modules' tab from within your Course
Step 3: On the right hand panel under the modules, select to either 'Duplicate existing module' or 'mirror existing module'
Duplicating an existing module creates an exact copy of the module in your course. Editing this module won't effect the original. Note: Duplicating creates an unpublished copy. You must publish the module before it will be visible in your course.
Mirroring an existing module makes a link to that module into your Course. Changes made to this module will be reflected across every instance of this module in every Course it is available in.