The main prerequisite for a student who wants to undertake the study of Calculus is an understanding of functions.  It is the context of functions that brings coherence to the study of Algebra and provides the connection between Algebra and Geometry, especially through the graphical representation of algebraic expressions.  Since Calculus is basically a tool for understanding how functions of various kinds model real-world behavior, a solid understanding of the basic functions makes the applications of Calculus considerably easier.  Any time you spend in this chapter strengthening your understanding of functions and graphs will pay off later in the course.  (Taken from an excerpt in the fifth edition of the Finney, Demana, Waits, Kennedy, and Bressoud textbook Calculus - Graphical, Numerical, Algebraic.)