After starting the ybcli, you can type help to return a list of command categories. Type help command_name to see the syntax and description for a specific category of commands (such as blade or manager). Type the next keyword in the command to restrict the output to the syntax for that command (such as manager reboot).
help [ command ] [ keyword ]
For example:

Available YBCLI commands. Type 'help <command>' for details                        
blade  config    debug  health  log      quit    system
clear  database  exit   help    manager  status
YBCLI (PRIMARY)> help manager

       manager reboot [ local | remote ]
       manager reset [ local | remote ]
       manager resume [ local | remote ]
       manager shutdown [ local | remote ]
       manager standby [ local | remote ]
       manager status [ all | local | remote ]
YBCLI (PRIMARY)> help manager reboot

	manager reboot  [ local | remote ]