You are greeted with a non-functional example screen but choosing either the Simple or Expert tab to enter your interval and command is a much easier way rather than using weird UNIX keystrokes on the command line.
If you want to make sure the end result will run when you want it to check out this web page. Enter in when you want things to happen and it will output the correct crontab entry so you can see what it should look like. It's a great web tool to check your crontab file and ensure it's doing what you want. There are other GUI cron editors out there so if CronniX isn't for you feel free to check out Crontooie, or Lingon.
Give Cronnix a try the next time you want to schedule a recurring or one time job to run while you are away from your computer.