Just to emphasize...when you check in, you don't have to print your boarding passes. I often don't have a printer handy. It is not a problem. When you get to the airport, go to one of the self-service stations, enter your confirmation number (or swipe your credit card so it reads your name) and pick the option to print boarding passes. Your boarding number is the same as if you had printed the boarding pass when you checked in.
If you are checking luggage, you can print your boarding pass during the check luggage process. It is easy!