Focal Length

Focal length is the basic description of a photographic lens. The focal length tells us the angle of view—how much of the scene will be captured—and the magnification—how large individual elements will be. The longer the focal length, the narrower the angle of the photo will be and the higher the magnification. The shorter the focal length, the wider the angle of the photo will be and the lower the magnification.

Focal length is how far in/out the lens on the camera is zoomed. It essentially  crops part of an image out so it isn’t in your final product. Below is a table I found of different ways you can use focal length and what length best suits what environment/style of photography.