C# Windows Form Navigation - Total Beginner

I have some programming experience with VB and lots of T-SQL - but this is my first venture into a C# Windows Forms project.

I need a main form and 4 forms that open and close from the main form. The method I want to use is to hold a reference to a form, as per the code below. The problem is that I have tried to add this code to my project and it won't even compile, so I'm obviously doing something very wrong.

I would like a step-by-step guide of hos to get this mechanism, i.e. where do I put this code. I am a little familiar with creating classes and forms etc, just some help in getting this to work may turn on the light for me.

http://stackoverflow.com/questions/3005732/showing-a-hidden-form

The first person who can give me specifics as to how I can implement the above mechanism in a C# Windows Form app gets the points.