Access the Control Center by swiping up from the bottom on the Home screen of your phone.
In the Control Center, there is an icon with the image of a flashlight on the bottom left. Tap this icon to turn the flashlight on. When turned on, the icon is white.
Be sure to turn off the flashlight when you are finished with it. When turned off, the icon greys out, indicating that the flashlight is no longer in use.