Why do people form queues?
The short answer
A queue is a way to share access to a limited service or resource. If people agree that those who arrive first are served first, they do not need to negotiate the order every time.
What a queue solves
A counter, seat, or ride may not be available to everyone at once. A queue makes “who is next” visible and creates a predictable way to share waiting time.
Not every queue is the same
Some systems use reservations, tickets, urgency, or priority seating instead of a simple first-come-first-served rule. The useful part is that the rule is understandable and the next turn is reasonably predictable.