Look at the Chinese character in the grey box. Find the pinyin and meaning that matches that character, select it and hit “Check my answer”—if you don’t know, choose the “I don’t know” option (don’t guess or cheat.) Rinse and repeat. BC[1, 2, 3, 4] are all the words learnt in each Beginners Class, IC[1, 2, 3, 4] is for Intermediate Class, and AC[1, 2, 3, 4] is for Advanced Class, as offered by the Confucius Institute using the 当代中文 textbooks.
This works on the Leitner flashcard system of spaced repetition: as you answer a card correctly, it will progress from the first, unhappy (>_<) bucket into the middle, that’s-not-too-bad (o.o) bucket. Later on, if you answer that same card correctly again, it will progress into the final, happy (^_^) bucket. If you answer a card incorrectly, it will go back through the buckets towards the unhappy bucket.
Optionally, if you want to play for reveals, choose a style (Cute animals, Ladies, or Men will show images of each of those things) and it will show you a black grid of boxes. For every correct answer, a black box gets removed, revealing a portion of the picture underneath. Once all black boxes are removed, you get to see the image for five seconds before the system resets. Because the images are grabbed randomly from tumblr feeds, if there’s something wrong with tumblr or the feed, the image may not show -_-
If you’re looking for it, the old version is here, but it is no longer being updated with the newer words, so it tops out at IC4. Besides, this version is cooler!