The document provides an overview of the concept of derivatives. It states that a function is differentiable at a point if the slope of its tangent line at that point is well-defined. It also notes that a function is differentiable over an interval if it is differentiable at every point in the interval. The document then discusses how derivatives can be systematically calculated by taking the derivatives of basic functions like power, trigonometric, logarithmic and exponential functions, and understanding how derivatives behave under operations like addition, subtraction, multiplication, division and function composition.