八is the kanji for the number eight. 八also has another common reading よう, which you will see in words like 八日. The shape of the kanji is considered lucky in Japan as it widens at the bottom (すえひろがり), suggesting prosperity.
That is how Fuguro works. It brings 八 back for review right before you forget it, each time a little later, until it sticks for good. You hear it spoken aloud, and you meet it again in stories you can already read. The first five levels are free.