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The shell boots reading its global configuration (to a file in the / etc), then by reading the configuration to the user (in a hidden file whose name starts with a dot, located in the directory the user base, ie / home / nom_de_l_utilisateur / .fichier_de_configuration), and then it displays a command prompt (in English prompt) as follows:

Machine: / directory / current $ defaults in most shells prompt consists of the name of the machine, followed by a colon (:), the current directory, and then a character indicating the type of user connected:
"$" Indicates that this is a normal user
"#" Indicates that this is the administrator, called the "root"

A command line is a string consisting of a command corresponding to an executable file system or to a shell as well as arguments (parameters) Optional:

Ls-al / home / jf / In the above command, ls is the name of the command, et al / home / jf / are arguments. The arguments begin with - are called options. For each command there are usually a number of options that may be detailed by typing one of the following commands:
-- Help
Command-?
Man command
When executing an order, a process is created. It will open three streams:

Stdin, called standard input, in which the process will read the input data. Default stdin is the keyboard; STDIN is identified by the number 0;
Stdout, called standard output, in which the process will write the output data. Default stdout corresponds to the screen; STDOUT is identified by number, 1;
Stderr, called standard error, in which the process will write error messages. Default stderr corresponds to the screen. STDERR is identified by the number 2;