We use a special Q&A website in this class called Piazza; it's like a StackExchange that's just for our class. For this step, just go to our class's Piazza page. If you can see a post called “First post!” there, then you're all set. If not, just sign up there with your PA email address.
There's no hand-in for this step; I'll check that you're signed up by looking at the enrollment on Piazza.