Most of the time there is a need for more than one type of content on a website. We usually see a newspaper website that contains news, pictures, videos, and forums sections. In terms of Drupal, a node is a piece of content, and every piece of content belongs to a unique content type, a content type that can contain various configurations and settings to define its own composition and behavior.
It is similar to a pancake maker, we set up a pancake maker to make a red bean pancake. Once we turn it on, it will keep making the same type of red bean pancake again and again. It will not suddenly make us a strawberry pancake, unless we use other ingredients and set up the pancake maker to create another type of pancake.