DALLAS—Give Southwest Airlines credit. The lighthearted airline that cracks in-flight jokes can make even the most dramatic changes seem like a win for all travelers. The airline paraded people through a shiny new Boeing 737 MAX 8 decked out with rows of cushy extra-legroom and “preferred” seat sections,

It's the end of Southwest Airlines' open seating era. Customers will be able to get assigned seats and and pay for extra legroom. Here's what to know.

Southwest Airlines executives have unveiled their vision for turning the carrier into an airline that gives passengers assigned seats, charges them extra for more legroom and offers red-eye flights but bags still fly free.