Alvaro, you get the boarding pass when you check in. You can check in online, if you have a Skymiles account, up to 24 hours in advance of your flight, and then go straight to the gate. If you have checked baggage, you can check in at the airport at either the computerized kiosk or the traditional line, and receive your boarding pass.
If you need another receipt for the ticket price or itinerary, you can get one printed out at the kiosk or the counter.
"In God we trust, everyone else bring data"