Using Commands' Built-in Help
The most common way to learn about a command is to read its built-in help. Many commands support an option that displays information about the command, and almost all commands display a usage message (saying how they are best used) if they are invoked with improper arguments or options.
Built-in help is terse, often consisting only of a usage message using the format shown in Figure 3.2. Still, it is easily available and often reminds you of the available options and required arguments.
There isn't a consistent way to get built-in help from commands, but there are several ways that work.
To see the built-in help from a command: