What is a Histogram?? Why do I need to know about this??

Over the years of photography many photographers make "Histogram" more complicated than it needs to be. So what is Histogram? It shows the amount of tones of particular brightness found in your photograph ranging from black (0% brightness) to white (100% brightness). Or in other words it will show your image and give a chart with pixels and depending on the lighting of your image it will give a range on how dark something is or how light something is. Why would I need to know this? You might have perfect lighting but when taking a photograph it could show something else. Many cameras will have a alert or notification saying this image needs to be darker or lighter.