First, why should you use a lens hood? A lens hood is a carved shape that is place in front of the lens, it blocks and defend the stray of light that can cause flare in your photos. It helps protect the lens from damage especially when you accidentally hit a hard surface.
This tutorial video from https://www.youtube.com/watch?v=B_m0MfAjNsk will show you why, when, and how to use a lens hood.