Now that the iPhone 11 Pro comes with three cameras, many do not understand exactly what the difference between them is. Basically, the answer is the lens they have in front of the sensor because the rest of the functionalities are very similar in terms of the quality of the images they can take or the quality of the video recording, up to 4K resolution and at 60 frames per second. Although three identical cameras may appear externally, one is of the wide-angle type, which is what we call normal , another is of the telephoto type, which brings things closer to the bottom and that several iPhone models have had for three years , and the third is the new ultra-wide-angle type, which allows to include a larger scene in the frame of the photo.
In the case of the iPhone 11, the situation is a bit special because Apple has opted for a wide-angle (normal) camera and a new second camera that, instead of being a telephoto lens as in previous iPhone models with two cameras, is Ultra wide-angle type, like the third camera of the iPhone 11 Pro.
If you want to understand exactly the difference between each of the three lenses, with this short video that Apple UK has posted on its YouTube channel, you can see how the same scene changes in just a few seconds.
https://youtu.be/yUmL7XoGy3w
Summarizing the situation a lot, now with these three lenses you can choose how to best frame your scene without ever losing image quality, you can for example take family photos with many people indoors where everyone can enter the image, and you can also take a photo with all three lenses at the same time so that you can then enlarge an image without losing quality, moving from the photo of one of the lenses to the other automatically, in a new functionality that Apple has called Deep Fusion. This will come later with the release of iOS 13.1, shortly after iOS 13.