Content Summary : Welcome to the third and final lesson for this tutorial. If you've gone through Lesson 1 and Lesson 2 , you already know the essentials for installing and writing useful scripts with MySQL and PHP. We're going to look at some useful PHP functions that should make your life a lot easier. First, let's look at include files. We all know the basics of includes, right? Contents of an external file are referenced and imported into the main file. It's pretty easy: You call a file and it's included. When we do this in PHP there are two functions we need to talk about: include() and require() . The difference between these two functions is subtle but important, so let's take a closer look.