Is there a way to track which lessons I've completed or used?
Edited
Yes!
Scroll down the bottom of the lesson and click the "COMPLETE" button
You will be prompted to confirm if you want to complete the lesson. Select "Yes"
You will then receive a success message.
The next time you open this unit it will take you to the next incomplete lesson but you can always go back and do a lesson again.
You can check your progress through the unit in the top right corner.