How can I list the existing cron jobs in my system, and then how can I add my script to the cron jobs list? Thanks.

Depends from system to system

crontab -l (lists all the jobs)

crontab -e (edits, make sure EDITOR is set)

~Sage

Thanks, crontab -e opens right up.

Whilst you can edit the crontab directly, you may want to consider keeping past versions.

Example:
UID=unixuser

1. Logon as 'unixuser'
2. cd $HOME
3. crontab -l > $LOGNAME.crontab
4. crontab -l > $LOGNAME.crontab.[yymmdd]
   
   
5. vi $LOGNAME.crontab (update your crontab file)
   
   
6. crontab $LOGNAME.crontab (uploads amended crontab file)

Just a suggestion.

Cheers,
Cameron