filename=`date '+%m%d%y'
This gives the current date to the filename so you can keep track of them.
chmod +x /mnt/backup/backup.job
This makes the backup.job executable so cron can run it.
export EDITOR=vi
crontab /etc/crontab
crontab -e
This just makes it automatically open the vi editor when you make the next statement. You only need to do this when setting it up.
I guess 00 06 * * * /mnt/backup/backup.job
Yep, that's for 6am and "00" is for no minutes. If you had a * in the minutes column, the job would run every minute of the 6am hour.
"is for 6am but what are the other 00's and ***'s for and where is my personal crontab? cron.daily, cron.monthly? etc"
The other *'s are for day, week and month
This just one way of doing things, as usual in Linux, you can use other methods. One is to put the script into the /etc/cron.hour folder and then edit the /etc/crontab to include the 06 line.
You also can set it up using Webmin.