People often assume that Calculus is one of the highest levels of math, the peak of mathematical knowledge that few can attain. Although the general populace does not get to calculus, it truly is simple, interesting and even useful! Calculus can be thought of in a simple way. Ever find the slope (rise over run) of a line? I am sure you have, especially a straight (called linear) line. But ever tried to get the slope of a curved line? Probably not, at least not exactly as the slope changes all the time! But calculus takes an equation, such as x², and changes it to find the slope. For this equation the equation now looks like this, 2x, and it is called the derivative. If you plug in any value into x, it will tell you the exact slope of the curved line x²! You may ask why it matters, well if you replace the y axis with "time" and the x axis with "position" suddenly the calculus equation doesn't just show the slope, it shows the speed. If you find the derivative of 2x, which is 2, you now not only know the speed, but the acceleration! This is used all the time.
Now a quick example of the power of calculus. Before Walmart was big, they were just a regular grocery store...until they hired mathematicians. They took their inventory, made the change in inventory into an equation and starting taking derivatives! They could then see the speed they were selling each item and the acceleration of the selling rate. They always knew how much to order! Using this technique they saved tons of money, could sell cheaper product and they made it big.
Calculus, its interesting, useful and endlessly applicable.