Flying out of Philadelphia. So it should show up on the app. A few days before or now?

I wasn't sure if I should print out my itinerary or something. Yes, I do have to check bags; so what I've read I can check in at the desk or on the kiosk, and all I need for that is my confirmation code. Then I would have to check my bags at the desk. If I have a connecting flight, would I get TWO boarding passes; one for my first flight and one for my second flight?

Lastly, going through security, all I need to show them is my ID, and boarding pass?

Thanks again for all the help. It's a bit confusing for my first time.