Do you want to study without internet Access?
If you are a Premium user is easy!
Go to the app in online mode, click on the unit you're interested in.
Once you open the unit, you will see a small cloud, on the upper-right corner.
Click on that icon and download the unit .
In offline mode, you will be able to start studying the unit you' ve downloaded.
If you want to delete the unit you have downloaded, go to the app Menu and click on Delete content.