The "help" command:

Usage: fossil help TOPIC
   or: fossil TOPIC --help

Display information on how to use TOPIC, which may be a command, webpage, or
setting.  Webpage names begin with "/".  To display a list of available
topics, use one of:

   fossil help                Show common commands
   fossil help -a|--all       Show both common and auxiliary commands
   fossil help -s|--settings  Show setting names
   fossil help -t|--test      Show test commands only
   fossil help -x|--aux       Show auxiliary commands only
   fossil help -w|--www       Show list of webpages