How to add a cron job for drupal on linux server

In the command line type

Press your insert key.
Insert a line, run every five minutes for example (more on syntax http://unixhelp.ed.ac.uk/CGI/man-cgi?crontab+5)
">http://yoursite.com/cron.php [/geshifilter-codes]

And now exit: press escape and type ":exit"
By exiting you are saving and you wont be prompted.