ちゃん is a familiar and affectionate honorific suffix. It is a baby talk version of さん and is primarily used for children, female friends, pets, and loved ones. It conveys a sense of cuteness and closeness.
That is how Fuguro works. It brings ちゃん 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.