You can start using the Dojo after you learn your first 50 words in Drops.
Currently, you can practice the words you need to practice most in the Dojo using 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. It means that based on your personal SRS score, you know the words you learned in Drops well enough not need a 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 get back to us!