help [command [subcommand]|expression]

Without argument, print the list of available debugger commands. a When an argument is given, it is first checked to see if it is command name. For example, help backtrace gives help on the backtrace debugger command.

Some commands like info, set, and show can accept an additional subcommand to give help just about that particular subcommand. For example help info line gives help about the info line command.