(Kinda stupid) Question about the director(s)

I’m really trying to get into theater, but I’m kind of confused about the role of directors. I keep hearing that they handle the visual aspects of a show, go over the script, and make sure everything looks good, but I’m wondering what happens when everyone pretty much knows what to do. Like, if the cast already understands their characters and the story, what does the director actually bring to the table? How do they make a production stand out or add their own vibe to it? I want to get a better grasp on what makes a director’s job so important, especially when it seems like a lot of the work is already done. Any insights about what they do behind the scenes would be helpful!