Here's a fun game. Have you ever played Follow the Energy? For example, depressing keys on your keyboard takes energy. Where does that energy come from? Well, the work performed by your fingers of course! But where does that energy come from? Well, the muscles in your fingers, of course! But where does that come from? Well, your food! But what about that? Well, your food's food! That? Eventually plants. That? The sun! That? Nuclear fusion. That? Gravitational potential! That? Etc...
But here's the funny thing. In this image, it kind of seems like energy gets "used up". The sun provides energy to the earth via solar radiation; the plants consume this energy; animals eat the plants, obtaining their energy; etc. However, energy is conserved. What gives?
Better yet, if the earth were not radiating just as much energy as it received, it should be heating up. However, the earth-atmosphere system is mostly constant temperature! This implies that the total energy flux is zero. If X Watts (Energy/Time) is coming in, then the earth actually radiates out X Watts as well.
So... if the total energy flux is zero, then how does your keyboard key actually get pressed? What gives?
The key is entropy. X Watts of solar radiation impinge upon the earth, but these photons are "hotter" (i.e. higher frequency) on average than those that radiate out. The balance is in numbers. You need more cooler photons to balance the energy of the hotter ones. E=hf; energy (E) is proportional (constant h) to frequency (f), after all.
This means that while energy is conserved, the flow of that energy increases the entropy of the system. In a very real sense, typing on your keyboard happens because of the waste heat generated in the process.
All driving us closer to Heat Death...