It's free of charge, but then you have to do some kind of "timebanking":
"Timebanking
Timebanking is a way to make language exchange fair for everyone. If you share your native language with other Langademy users, you earn the same amount of time for practicing other languages in your Time Bank account. And when you practice a language that is not your native language, you spend time from your account. You will start with 5 hours, and every month, you will receive a free recharge of 2 extra hours."