Many services provide you with ready-to-share GIF for sharing on social networks and chat apps, but there are little services to create those images, and if they are based on converting a ready-to-play video, Facebook will make you visualize your real life animated picture.
By entering the camera icon or dragging to the left you will find a GIF option at the top to switch to. You can take a very short video of a few seconds and view it as a moving picture.
Facebook does not just create an animation, but you can add effects and filters to them with different frames, and then you have the freedom to act on the resulting GIF such as sending it as a deleted story after 24 hours, posting it on your profile or saving it on your device.
It is worth noting that the feature is currently available to a limited number of users and is specially monitored on the iPhone and will be gradually available to all and reach the Android system.