The mu help command lists all available options and command names along with short descriptions of what each of them does. It is similar to the mu --help option.
A command name can be supplied as an argument to help, in which case it will display a help page for that particular command, e.g.:
mu help ldflags
will output help for the ldflags command. It is synonymous to the --help option used with that particular command, e.g.: mu ldflags --help.