what is calculus ? or defferentiation? or derivatives?

Question

What is the purpose of them? When do we need them? What is it related to? What does it do actuall?

Answer 1

Calculus deals with derivative and differentiation.  By definition, the derivative is the slope of the tangent line passing through a single point.  It is also referred as the rate of change.  Calculus can be used in many applications.  You can use it to find the point in time where something reaches it peak (maximum or minimum).