知る is a ごだん (Type I) verb meaning to know or to find out. It focuses on the acquisition of information. To express the state of knowing, the form 知っている must be used. It is distinct from 分かる, which implies understanding or comprehension.
That is how Fuguro works. It brings 知る 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.