The direction of movement (up or down) can be permanently the same, or be controlled by personnel according to the time of day, or automatically be controlled by whoever arrives first, someone at the bottom or at the top (of course the system is programmed such that the direction is not reversed while somebody is on the escalator). In the last two cases there has to be an alternative nearby.
Charles Seeberger developed the escalator and installed the first one as an amusement ride at Coney Island, New York in 1897. He joined the Otis Elevator Company and they produced the first commercial escalator which won a first prize at the Paris 1900 Exposition Universelle[?] in France.
Escalators in the London Underground used to have wooden steps, but this was changed after the King's Cross fire at King's Cross station in 1987. Escalators now have metal steps in a continuous loop that move on tracks. Escalators are typically used in pairs with one set going up and another going down.
Escalator was originally a trademark combining the words escalade (an old term for using a ladder to scale a wall) and elevator.