This is an introduction of functions.  A function is a correspondence or rule that assigns to every element in a set D (the domain) exactly one element in a set R (the range).  It deals with domain, range, and how to graph them.  You also learn operations of functions, such as addition and multiplication, and compositions. What are compositions of functions?   Well, it is where you take two functions and combine them to get the composition.  This may sound difficult now, but once you get into this section, compositions will become more clear.