How would you describe calculus in simple terms? I keep hearing about this weird type of math called calculus. I only have experience with geometry and algebra. Can you try to explain what it is to me?

One of the greatest achievements of human civilization is Newton's laws of motions.  The first law says that unless a force is acting then the velocity (not the position!) of objects stay constant, while the second law says that forces act by causing an acceleration (though heavy objects require more force to accellerate).
However to make sense of those laws and to apply them to real life you need to understand how to move between the following three notions:


*

*Position

*Velocity (that is the rate of change in position)

*Acceleration (that is the rate of change of the velocity)


Moving down that list is called "taking the derivative" while moving up that list is called "taking the integral."  Calculus is the study of derivatives and integerals.
In particular, if you want to figure out how objects move under some force you need to be able to integrate twice.  This requires understanding a lot of calculus!
In a first semester class you usually learn about derivatives and integrals of functions of one variable, that is what you need to understand physics in 1-dimension!  To understand the actual physics of the world you need to understand derivatives and integrals in 3-dimensions which requires several courses.
