Have you tried placing your laptop on your lap and felt the warmth after a few hours? That is your laptop saying that it isn't a perfect tool. They can't utilize every energy that is fed to them. The heat that you feel is the energy that escapes from them. They're energy that failed to transform into a usable form. So, you have to cool them down to calm them and to lengthen their working mood.
Now, to tame down your laptop's components' hotness, there are heat sinks and cooling fans. Heat sinks are these pieces of metals placed side by side the components and these metals absorb the heat from your component and dissipate it into the air. The CPU cooling fans help in the dissipation process.