ls : Displays list of files in the present working directory.
cd directory : Changes directories .
passwd : Changes the password of current user .
file filename : Displays file type of file with name filename .
cat textfile : Throws content of text file on the screen
pwd : Shows present working directory
exit or logout : Leaves the session
man command : Read about command on man pages.
info command : Read about command on info pages.
apropos string : For searching database for strings