Help screens
From Joomla! Documentation
The Joomla! Administrator includes an integrated context-sensitive help system that accesses pages in HTML or XML served from a directory within the Joomla installation, or more commonly, from an external help server. The documentation wiki contains the "master" help screens for all Joomla versions from 1.5 onwards. The following pages gather together the help screens for each version.
Joomla! 4.1 help screens 
Joomla! 4.0 help screens 
Joomla! 3.10 help screens 
Joomla! 3.9 help screens Support has ended
Joomla! 3.8 help screens Support has ended
Joomla! 3.7 help screens Support has ended
Joomla! 3.6 help screens Support has ended
Joomla! 3.5 help screens Support has ended
Joomla! 3.4 help screens Support has ended
Joomla! 3.3 help screens Support has ended
Joomla! 3.2 help screens Support has ended
Joomla! 3.1 help screens Support has ended
Joomla! 3.0 help screens Support has ended
Joomla! 2.5 help screens Support has ended
Joomla! 1.7 help screens Support has ended
Joomla! 1.6 help screens Support has ended
Joomla! 1.5 help screens Support has ended
Comprehensive information on how the Joomla help system works, how administrators and site builders can configure it and how developers can make use of it in their own extensions can be found here: Help system
Usage data for the help screens 
can be found here: Most visited help screens