There should be something interesting you could offer that isn't going to ruin the story right? The synopsis/description is pretty much like a movie trailer. Just think of, say, the trailers for Ralph Breaks the Internet. They show the Disney Princesses, they show Ralph and Vanellope going to the internet, meet various characters, etc. Maybe, give us the stakes of the story. What are they going to lose if they fail. This is not something that ruin the story for knowing in advance since it is one of the very first thing a reader would know. You could also tell some of the more direct result when Earth got booted up into the magical world. What are the immediate consequences? How did the people reacted? Things like that. Really, just present something about your story that tells your readers how great it could be. Something that would interest them. Something to differentiate your story from the other stories. Just something that makes them want to read your story.