The Time Rewind feature allows your camera to take burst shots for two seconds before you press the shutter button. In effect, you get a timeline of photos where you can select the best image to save in your device.
To capture photos using Time Rewind mode, tap

from the Camera app, then tap
Time Rewind.

After you pressed the

button, Time Rewind lets you select from the burst photos that your camera captured.

To automatically select the best photo, tap Best. To manually select a photo, move the round slider then tap Done.