It is not probably a topic that has you glued to the edge of your seat with anticipation, but few accessories can have a more universally positive effect on your image quality than a lens hood. If you are new to photography, this helpful video will explain how they work and why so many photographers use them.
Coming to you from steele training, this video is an oldie but goodie that gives a helpful introduction to lens hoods. At their most fundamental level, lens hoods exist to stop off-axis light outside the field of view from entering your lens. When it does, it bounces around inside your lens, reducing contrast and causing flares, neither of which are desirable unless you are specifically intending to get a very stylized look. They are also useful simply because they provide a physical barrier for the lens to give it a bit of protection from the front and sides. I can't count how many times I've accidentally bumped something with the end of my lens, and had the hood not always been on, it would have been the precious front element bearing the full brunt of those impacts instead. It's quite the useful little piece of plastic. Check out the video above for the full rundown.