ある primarily means to exist, to be (located), or to have for inanimate objects. It is a foundational verb used to indicate the presence of things that cannot move on their own, such as objects, places, or abstract concepts.
That is how Fuguro works. It brings ある 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.