勉強means study, learning, or diligence in English. It commonly refers to the act of devoting time to gaining knowledge, such as doing schoolwork or preparing for exams. When used as a verb (勉強する), it means to study or to learn.
That is how Fuguro works. It brings 勉強 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.