Plugins are the best way to extend QGIS, as they can be easily updated and reused by other people. And as we'll see throughout this book, you can use Python to create plugins. When you create a Python-based plugin, you can usually access that plugin's functionality through the PyQGIS API.
The easiest approach to creating a plugin is to use the Plugin Builder plugin to jump-start development. You can find it in the main QGIS plugin repository and install it.
Perform the following steps to create a simple plugin that displays a dialog box with a custom message: