cron jobs is runs at a certain time on a unix system
The command "crontab" is used to set a file to execute at a regular basis
the command "at" is used to execute on a specific time.
To find out more in Your environment use the command
# man at
# man crontab
There must also be som setings in /etc/cron.allow
to allow another user then root to run the command.
Also the cron deamon must be started
MIME type . Used with filenames as the extension like .jpg .php .html
The sets what program is used to open the file.