What is the difference between the different focal lengths?
A lens with a focal point ranging from 7.5 to 15mm is also called a fisheye lens. In this case, the distance between the sensor and the center of the lens, also called the focal length, is very short. A fisheye lens with a focal point starting at 16mm will have an image angle of about 100 degrees. This means you can see a lot on the photos, but in a circular shape. The subjects on your photo will also be morphed, which creates a fun visual effect.
With a lens ranging from 12 to 35mm, you have a short focal length that creates a large image angle. This focal length allows you to capture a large part of the environment. Similar to a fisheye lens, these lenses also slightly warp the image a bit. Objects that are further away will appear smaller, while object that are close will appear larger. You can use this focal length for interior photography, as at will make rooms appear to be more spacious.
Lenses with a focal length of about 50mm are also called standard lenses. The distance from the sensor to the lens creates an image angle that's roughly equal to the image we can perceive with the human eye. A standard lens with zoom functionality is able to bring subjects closer thanks to a larger focal length. At the same time, you have the option of taking photographs with a wide-angle, without warping the the image too much. As such, a standard zoom lens is suitable for many types of photography.
The difference between these focal lengths may seem big, but all of these numbers belong to the 'macro' category. A lens with a focal length starting at 35mm lets you capture even the tiniest details, starting at a distance of 3 centimeters. Lenses starting at 60mm allow you to take detailed close-ups from a distance. The larger the focal length, the further the distance between you and your subject. A macro lens is suitable for taking photos of insects and flowers. Additionally, 88mm lenses are suitable for portrait photography, without creating a warped image.
A focal length between 70 and 300mm lets you zoom in on objects that are very far away. These types of lenses are also called telephoto lenses. The result of a large focal length is that you have to work with a very small image angle. A 300mm lens has an image angle of less than 10 degree. You actually only use these lenses if you really can't get closes to your subject. Take animal photography or professional sports photography, for example. Lenses with a large focal length are relatively expensive.