A Trip to the Moon, or Le Voyage Dans la Lune in its original French, is the first ever science fiction film. It is 14 minutes long, and silent, but narrated by an in-theater narrator.
A group of astronomers agrees on an ambitious plan to land on the Moon. They construct a massive gun to fire a bulletship to the moon. Their plan is successful, leading them to explore the strange other world inhabited by the Selenite civilization. Once their they are captured, but they do escape back Earth.
Le Voyage Dans le Lune is actually based on two early science fiction novels dealing with travel to the moon. One of these was "From the Earth to the Moon" by Jules Verne, which deals with the Gun Club making a giant gun to fire a bullet-ship into space (a scientifically possible idea, but less practical than current space travel technology) and "The First Men in the Moon" by H.G. Wells, which details the inhabitants of the moon, including the Selenites.