You can start using the Dojo after you learn your first 50 words in Drops. The Dojo can be found in your Topics list, after Travel Talk. In order to find it, please make sure you have the latest version of the app installed on your device.
Currently, you can learn the words you need to practice most with the Dojo, our Spaced Repetition System (SRS). This optimal learning algorithm predicts when you need to encounter a word to maximize the probability of you memorizing it.
The message "no words available for optimal learning" means, the system estimates there are no words you need to practice for memorizing at that time. Based on your personal SRS score, you know the words you learned in Drops well enough not to need review at that time.
You need 50 words to unlock the Dojo. Characters do not count as words for the Dojo. If you have more than 50 words learned besides the characters, and the Dojo is still unlocked, please contact our support team.