The last sections of the article show you how to create a NetBeans plugin from scratch. These sections are prefaced by these words, which I thought were quite nice:
"After trying out the previously discussed NetBeans plugins and others that you download from the NetBeans Plugins Portal, you'll probably want to create your own. If you're new to this task, you might find it somewhat intimidating. Fortunately, NetBeans greatly simplifies plugin development."
Go read it, right now!