Bringing a fresh portion of film into position is not as easy as it may seem on first thought. How much film should be transported to ensure that the second picture is not taken over a part of the first one or to prevent that a lot of expensive film between each picture is not used? And then, how is it communicated to the photographer that enough film is transported? Also the photographist should know how much pictures are left to be taken. How is this communicated to her or him?
Many inventions were made to answer these questions. A very good and simple answer that was used for more then half a century is seen in this video of a daylight loading roll film in a camera with front roll construction. The spools (feed and take up) are located in the front part of the camera, where there is enough room to the left and right of the incoming light rays. Before this so called front roll design was used, the spools were located behind the plane of focus, making the camera about one third longer.
The film consists of a light sensitive film and a opaque protection paper band. On the back of this paper band, numbers are printed at a certain distance. These numbers can be seen in a window in the back of the camera. If the next number appears in the window, enough film is transported. Also the photographer knows how much pictures are left.

The video shows a No. 2 Plico camera from 1899 to 1913, with the side panels taken off. It is the European version of the No. 2 Flexo. You are looking at the back and side of the boxcamera. The clicking sound is the noise of the ratchet wheel, that prevents the film on the take up spool to rewind. Why the numbers on the paper band are up side down I don't know.

And in the second part of the video, for the education and entertainment of a whole digital generation (or two) who have never seen it in full action, is the famous red window. You can see the paper band moving in the window until the next number appears. The red window was first used in combination with a daylight spool and printed numbers on the protective paper in the 1892 Boston Camera Mfg. Co. Bull's-Eye. See the video of this camera for more information. 
The camera in this video is a No. 2 Folding Pocket Kodak (1899-1910).