Why does Dill and Jem want to give Boo Radley a note? What does Atticus do when he finds out about their plan?

They wanted Boo Radley to come outside so they could look at him. They attach a note to the end of a fishing rod as to not get too close to his house. Atticus admonishes them. He says that if they want to see Boo Radley, they can knock on the door and treat him like a human being and not a circus side-show. He also adds that Boo is entitled to his privacy away from the gawking eyes of kids.

they wanted to meet Boo.