The Myth of Sisyphus

At the end of Camus' "The Myth of Sisyphus" essay he says that we must imagine Sisyphus happy. Why do you think he says this and what does this mean?
Why does Camus say that knowing whether we are free or not does not matter? Compare this idea of freedom to Kant's argument in "What is Enlightenment." What sort of freedom is Camus interested in?