A film editor is like a person who puts together a really cool puzzle, but instead of puzzle pieces, they use video clips that people have recorded.
When a movie is being made, lots of people go out and record different scenes. Some people record the actors talking, some people record the pretty scenery or the cool special effects. All of these recordings are put onto a computer so the film editor can see them.
The film editor's job is to take all of these recordings and put them in the right order to make the whole movie. They make sure everything matches up, like the person who was standing on the left side of the screen in one clip is still on the left side in the next clip. They also make sure the sound matches up, like when the actor talks, their mouth matches the words they are saying.
Film editors can also make special effects and add music to the movie. They work really hard to make the movie exciting and interesting for people to watch.