For example, ls lists all files within the current directory. If a third option is required, the option string will then be three characters long. Your password is changed using the passwd command.
Most systems have on-line manuals, accessible using the man command.
For many commands, issuing the command itself without any arguments returns its usage. There are many ways to find out how big that file is. The first step is to create the directory. This is one way of using the cp command to do that. There are many variations, all as good as the one shown.