If you are seeing the following image:
it is because you are using a trial profile, and you have reached the end of the trial content available.
To continue learning, please visit https://learn.mangolanguages.com/ and click the "Upgrade Your Mango Profile" button at the top of the screen.
Once you've upgraded your profile you will need to log out of the app, then sign in again with your email address and password. After that you will be able to continue your language learning with Mango.