The name of a Linux command almost always consists of lowercase letters and digits. Most commands let you specify options or arguments. However, in any given case, you may not need to do so. For example, typing the w command without options and arguments causes Linux to display a list of current users. Options modify the way that a command works.
Most options consist of a single letter, prefixed by a dash.
For example, the -h option of the w command causes the output of the command to omit the header lines that give the time and the names of the fields. Arguments specify filenames or other targets that direct the action of the command. For example, the w command lets you specify a userid as an argument, which causes the command to list only logins that pertain to the specified userid. Because Linux provides so many commands and because Linux commands provide so many possible options, you can't expect to recall all of them. To help you, Linux provides the man command and the apropos command, which let you access a help database that describes each command and its options.