Watching movies is a great way to learn a foreign language. Movies let you listen to real conversations by native speakers and hear the way they interact in real life situations.
Most people use a kind of shorthand to speak to people they know, especially when they share a knowledge of a particular subject. This shorthand is difficult to reproduce in language manuals since it would take it too much time setting up the story.
Movies have time to set the scene. Since the setup, as well as the dialog itself, is in the foreign language, you get a very rich feel for the language and culture when you watch a movie.