Cron syntax and valid values:

   1  # +---------------- minute (0 - 59)
   2  # |  +------------- hour (0 - 23)
   3  # |  |  +---------- day of month (1 - 31)
   4  # |  |  |  +------- month (1 - 12)
   5  # |  |  |  |  +---- day of week (0 - 6) (Sunday=0 or 7)
   6  # |  |  |  |  |
   7    *  *  *  *  *  command to be executed

Below are a few examples on how to run a script every 10 minutes, every 30 minutes, every hour, daily, weekly, monthly.

Execute crontab -e and add the following (see man crontab):

   1  # Every 10 minutes
   2  */10 * * * * /home/belsebub/delete_old_stuff.sh
   3  
   4  # Every 30 minutes
   5  */30 * * * * /home/belsebub/delete_old_stuff.sh
   6  
   7  # Every 60 minutes
   8  */60 * * * * /home/belsebub/delete_old_stuff.sh
   9  
  10  # Every day at 00:00
  11  00 00 * * * /home/belsebub/delete_old_stuff.sh
  12  
  13  # Every saturday at 00:00
  14  00 00 * * 6 /home/belsebub/delete_old_stuff.sh
  15  
  16  # First day of every month at 00:00
  17  00 00 1 * * /home/belsebub/delete_old_stuff.sh

On Debian the configuration goes to /var/spool/cron/crontabs/username.