how do I turn the flashlight off/on?

On your iPhone 5s, PUSH UP from the bottom of the screen and that will reveal the Control Center. You should be able to locate the Flashlight icon. TAP on the Flashlight icon.

Axel F.

Either:

1. Hold your finger on the flashlight icon on the Lock screen for 1 second to toggle it
2. Open the Control Center and there will be a button for the flashlight

On the Home Screen you can simply press and hold the torch button for a second to toggle the torch.

Or, swipe up from the bottom of the screen to bring up Control Center (down from top right for face ID phones) and press the torch icon here.