(crontab -e) this command will open your crontabs
What is a crontab well it allows programs to start at a specific time so for instance the server goes down and your not around your program will restart at the timestamp you set.
#minute hour mday month wday command
*/1 * * * * /usr/local/bin/php /usr/local/www/new-user.php >/dev/null 2>&1
The line above with the new-user.php file starts every minute. And is run by php a prehypertext preprocessor. The line (>/dev/null 2>&1) makes sure there is no output to a terminal.