US airlines check your boarding pass before you enter the jet bridge, and that’s it — while many international airlines have flight attendants standing at the door of the aircraft who will look at your boarding pass again.
Flight attendants on most airlines around the world will see you’re on the right plane, direct you to the correct class of service, and tell you which side of the plane to proceed down in the case of a widebody. Although it’s common on single aisle aircraft as well.