You go to the website 30 hours before your scheduled take-off time, log-in and fill in the details requested. If you have already paid for seats and already have your seat numbers, then you can skip over that part. Once complete, you'll get an option to email your Boarding Pass to yourself and/or you can print it immediately.
When you arrive at the airport, you will go to a separate queue, usually called Bag Drop. No need to join the long queue of idiots who didn't bother to check in beforehand. In fact, I turn up later than everyone else, since I've already checked in and my seats are already chosen. When you get to any desk, the agent will see that you have already checked and ask you if you want them to print you out a boarding pass. You can say yes to this. It doesn't cost you anything and you are probably used to them, as opposed to scanning with your Smartphone.
The long queue is for people who haven't done this, so the staff have to add their passport details, allocate seats.....you get the picture.
So check in beforehand and then relax. You can take your time. No need to rush and join any long queue. Even if there isn't a separate Bag Drop queue, you can just take a seat and wait until the normal queue has diminished. There will be no advantage to you standing and waiting nor rushing to be first in the queue.