You can find Dojo in either the Home tab (under Review Tools) or the Explore section (under Review & Progress). You can start using Dojo after learning 50 words.
Dojo uses a Spaced Repetition System (SRS), an optimal learning algorithm that predicts the best times to practice specific words to maximize retention.
The message "no words available for optimal learning" means the system has determined there are no words you need to practice at that moment. Based on your personal SRS score, you have memorized the words you've learned in Drops well enough and no review is currently necessary.
Please note that characters do not count as words for Dojo.
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