Just hit the space bar to play the movie.
When QuickTime Player first opens, you get a very cool, borderless playback window. You can open a movie file by double-clicking it. Finally, when everything looks good, you can post your masterpiece to YouTube, Facebook, Vimeo, or another online site. Despite its name, QuickTime Player also lets you edit movies and even record new ones, either using your Mac’s built-in camera or by recording screen activity. The cornerstone of OS X’s built-in movie-playback software is QuickTime Player, which sits in your Applications folder.
Like any movie, it creates the illusion of motion by flashing many individual frames (photos) per second before your eyes, while also playing a synchronized soundtrack. A QuickTime movie is a video file you can play from your hard drive, a CD or DVD, or the Internet.
