How can I unlock courses?

If you want to unlock special courses in addition to basic access, you can do this directly via the menu if you are logged in.
Simply tap on the menu in the upper left corner of the app (three horizontal bars) and select "Unlock". Now you can choose between the different runtimes.
The purchase is processed via the respective app store (e.g. iTunesStore, Google Play, Amazon) and can be managed there.