The casing of the camera makes it durable by protecting all of the parts inside, and keeping them together. It also prevents light from hitting the film before the shutter opens.
The shutter opens and closes in a split second to expose the film to light. It controls how long the film is exposed in order to capture the image. It opens as soon as you take the picture.
The lens is the small, curved piece of glass or plastic in the front of the camera. It redirects the light onto the film in order to create the image.
The film is what the image is recorded on. It is light sensitive, so when the lens bends light towards it, the film reacts and records it. It has several layers that help it record colors. Each layer lets different amounts of light through to capture each separate color.