What do different mm lenses do and how do they affect the quality of the photographs taken?

Different mm lenses have varying focal lengths, which affect the field of view and magnification of the photographs taken. A lower mm lens, such as 18mm, captures a wider scene, while a higher mm lens, like 200mm, zooms in on distant subjects. The choice of lens impacts the composition, depth of field, and overall quality of the photographs by influencing perspective, sharpness, and background blur.