Without film there would be no picture. It's important to pick the type of film you want for specific situations!

Basically:

Film is a sheet of plastic covered with light-sensitive silver halide salts. When it is exposed to light the emulsion creates an invisible image on the film surface.

Types:

Black-and-White:

Black-and-white film is the original type of film used since Eastman Kodak invented the first flexible photographic film in 1885. It has only one layer of salts so when it is exposed to light, only clear and gradients of black remain, thereby making a negative.

Since black-and-white is the original and classic type of film, it is often used for important or "classy" events such as weddings. Black-and-white also has the tendency to smooth out imperfections and make a human subject look more "perfect." Black-and-white is used by professional photographers for its unique look and great versatility both in the camera and in the darkroom. Beginning photographers often use black-and-white when learning about printmaking because the developing/printing process is much simpler than color film development.

Color:

Color film uses at least three layers of salts unlike black-and-white's one layer. The layers of salts are made to be sensitive to certain colors of light. The most common layers are sensitive to blue, green and red. Higher end color film, such as Kodak's Kodacolor II use up to 12 emulsion layers and up to 20 different chemicals.

Color is this most popular type of film used today. Color photography is used in almost every field to capture the most life-like picture possible. However this film is harder to develop by hand because of its more complex chemical emulsions and extra steps that are needed to develop prints in the darkroom.