To Be A Superhero by Rachel Yu
Illustrated, very colorful children's book about how to be a superhero.
He invites you into his castle and asks you to take your shoes off.
You have to have an origin, a super power. There are many to choose from.
Some don't have powers but then there is a costume to pick from.
A mask is a good idea and so is a sidekick, like a friend or your dog.
Goes on to help somebody that called for help.