Geany's documentation is available in different formats.
HTML and text versions of the documentation are installed when you install Geany. Choose the Help->Help menu item to view the HTML version. The manual will be opened in a browser window (unless the browser command is not set correctly in the Tools tab of the Preferences dialog).
You can also read the manual online:
This documentation contains the most recent changes in Git, and will probably include some features not in the current release.