It's pretty straightforward. You simply write a bash script (or whatever shell flavor you like) to do the backups (either tar or dar commands). Then create a scheduled crontab event using:
I'm assuming you know how to input the lines in crontab. Here's an example from mine:
5 0-23/1 * * * /usr/local/bin/backup-full.sh /backup/users .users-backup 5 >> $HOME/backup-users-weekly.err 2>&1
This line runs my backup-full.sh script every hour at 5 minutes past the hour. Your scripts can be as simple or complicated as you like. Mine are a little complicated in that they look for hotplug events to migrate my backups and do checks to see when the last backup was performed and such. That's why I installed them to run every hour since they are on my laptop and it's not always powered on. So I let the scripts do all the checking instead of relying on my computer being powered on at the appropriate times. A place to check for some simple backup scripts is: http://www.linux-backup.net
Hope this helps.