Long before digital cameras and video recorders came into the scene, movies and photos were always recorded on film. A film is a special plastic sheet which is coated with some chemicals to make it sensitive to light. When the film is exposed to light, it records a change in the chemicals and when this exposed film is treated with a few more chemicals in a bath, a photograph can be seen on it. This is the case of a single film exposure. But when you need to make a moving image, or a video, a series of films are exposed to light (or the scene) at a particular speed which records a movie. This type of film is called analog film and comes in a few variants of sizes for the quality of the video and the projection size. Production of these types of photos and videos are very expensive and replicating them into multiple forms is far more expensive and time consuming.
Recording photos and videos on a digital camera has taken over the film industry, let alone our own personal lives. Being immensely cheap to produce and replicate, digital photography and video is now the future. But film is still here and will stay for a while till they completely go extinct. So do you know how analog films actually work? Check out this video which explains the same in detail.