First of all, you need to upload an app that can make it happen, and after that take a photo of an object, so this object could fit into the screen. After some time of rendering, you will get an automatic 3D photo.
An ability to take a 3D photo is installed by default in versions of iOS 13 and higher, so first you need to take a pic, and then the iPhone app can make a 3d out of 2D automatically.
You can’t always view them on your camera roll, because most phones do not support the formats of 3Ds. But it’s always possible when you share it to the platform that supports 3D format pictures.
You can view them after you save them in the app in the format your computer can read. After saving, a 3D photo will look like a photo but a volumetric one.