The first bit of the tutorial follows first principals. Without an understanding of integration and the whole concept what differentiation really is (which is very much 1st and 2nd year university maths) it is very difficult to understand exactly why first principals are used in calculus. For matric level, all you need to know is that when we are differentiating we are deriving the gradient of any function and/or expression. I really do not know why there is an emphasis on knowing first principals, but it is important and is a method you should familiarise yourselves with
long division, factor and remainder theorem
this is by far the one section that everybody loves to hate: be careful going through this tutorial and make sure that you understand everything that is being covered. it is not the most difficult concept to grasp, always think simple: you are working with division and factors and remainders, nothing more than that, the only difference is that now you have variables involved as well.
the cubic function is a simple function and I want you to think of it as nothing more than an extension of the parabola. In essence you are doing the same thing, except in this case you now have an easier tool to find the turning points as well as a new tool to find the x intercepts, but the principals are exactly the same.