Every movie begins with an idea that is translated into a screenplay. The screenplay may change over the course of the movie due to a number of factors ranging from the demands of a star to the death of a cast member to ideas that pop up as the story begins to evolve. Even movies that are said to be improvised like mockumentaries still have screenplays that work out specific scenes if not specific dialogue.
The part of the movie-making process where everybody shows up on a set and the cameras roll is called principal photography. Today, principal photography is likely to be the shortest part of the process. It can last as little as 2 weeks for a low-budget movie to 1 year for an epic. In cases where a movie and its sequel are being shot back to back, like "Lord of the Rings" or the final two "Pirates of the Caribbean" movies, principal photography may last longer than a year.
The effects stage of making a movie includes spectacular special effects such as you'd find in a science fiction movie, but it also includes less obvious effects that most movie audiences aren't aware of. One of the most common of these post-production effects is something called looping. Looping is the process of having an actor re-record dialogue in a studio that didn't record correctly on the set or location for some reason.
Editing is a very important part of the film-making process. Editing involves taking all the footage that has been shot during principal photography, applying the effects to it, and then placing it into an order that corresponds with the director's vision, or at least the screenplay. Editing is all about choosing which shots work best, and creating a rhythm and pace that reflect the tone of the story.
After the film has been edited, the composer creates the musical accompaniment to the scenes. Imagine how successful "Rocky" would have been without that rousing score. A great music soundtrack can mean the difference between a hit and a flop.