It used to be that when you flew, as soon as you made a reservation, you could choose your seat. These days, that’s changed. On Southwest, my favorite of all airlines, you get a letter and number assigned when you check in. You board in the order of your letter/number combination, from Group A1 to Group C 60 or something thereabouts. When you board, you choose your seat from those remaining.
This, that and the other thing 