Domain and Range by Shmoop

Domain and Range, two terms you will learn to love (or hate with a vengence). Domain is a number line for which all x values of a function lie in. Range is a number line for which all y values lie in. Basically, domain is all possible x, and range is all possible y values.

Here is some more help if you still don’t understand Domain and Range.
http://www.shmoop.com/linear-equations/functions.html