Using the 16/35mm Cine-Protractor helps you select what lens you want to use from the Wide-Angle 5.9/14.5mm lens (almost 90° Field of View!) through the "Normal" 25/50mm Lenses to the Telephoto 200/500mm Lens.

16/35mm Cine-protractor showing Lens Field of View angles. These are accurate to 0.1 degree.

Generally a "Normal" lens is considered to have less distortion and most closely represent what our eye sees. We could consider normal lenses to be 16-35mm in 16mm and 40-85mm in 35mm. The filmmaker Robert Bresson is famous for only using the 50mm lens for all of his filming.

Here is a picture from Bresson's "Lancelot du Lac":

Creative filmmakers can use different size lenses to create a different quality of look. Wide angle lenses are useful for showing wide areas and generally keep close and far areas in focus. Wide angle lenses could be from 16/40mmto 5.9/14.5mm in 16/35mm formats respectively. Notice how the couple and the background here are in focus.

Telephoto Lenses can be used to separate or isolate a subject from its surroundings. These "long lenses" could be considered from 41/100mm to 200/500mm in 16/35mm formats. Notice the background is out of focus.

This can be used to create a pleasing "Portrait" effect

but can also be used by filmmakers to suggest a sort of "characters alienation from their environment" as Michealangelo Antonioni is so successful at in his films like L'Avventura

The wide angle lens is often called the "democratic lens" as it allows the viewer to look at anything on the screen which is in focus which can allow for extremely long takes. Charles Chaplin, Buster Keaton, John Ford and Orson Welles were all masters of this technique. The comedians used it to create edge of your seat humour (like Chaplin rollerskating blindfolded near a 4 story drop in City Lights) or to create depth and detail as in Citizen Kane.

The major problem with wide angle lenses is they distort the image by bending, especially around the edges. This is seen in an extreme example of a telephoto lens.