That's not such a dumb question at all
To be able to create plugins you need to know how to program. If you are interested in creating your own plugins, take a look at
this page. It contains information about the plugin API. The plugin API is there to help you easily create new commands, new tags and new features for MSN Messenger and Windows Messenger.
Plugins can be made in a wide variety of programming languages, of which Visual Basic and C/C++ are the most used. However, plugins have also been made in Delphi. To help you make plugins for Messenger Plus!, sample source codes have been made. These are available in both Visual C and Visual Basic formats and can be found at the same page as mentioned earlier:
http://www.msgplus.net/help_plugins.php.