Imagine a glass of your favorite drink that never became empty. Now think about what really happens. You take a drink and there is less in the glass. You keep drinking and soon it is all gone. Good thing you have more to refill your glass. What if there would never be any more of your favorite drink. What would you do? Now you know the difference between renewable and non-renewable. Its too bad that many things here on Earth will run out. This includes some of our natural resources we depend on. Things like oil will not last forever. There is a limited supply. Someday, we will run out, so then what? At current rates of use, coal will last about 300 years. Petroleum will be used up in just a few decades. 
What are some examples of resources that will run out?
Electricity