You don't NEED to use it at all...
Using the serial input is only if you have EXTERNAL microchips that need to feed input to the robot controller. Some teams have shaft encoders and magnetic compasses that feed data to faster microprocessors. Then, the processors evaluate the data and send correction information to the Robot controller. The robot controller uses this info to correct its course.
If you don't know what it does, or what you're doing... the general rule is DON'T TOUCH IT. Messing with it will void your warranty, as stated in the manual. If you break it, you won't get a new one....
Don't get me wrong, I'm not opposed to trying new things. However, asking just enough questions so that you can tinker with it will only get it broken. I strongly suggest you read some manuals to [try] to fully understand how it works.
You can start at the
Stamp Documentation V2.0. Believe it or not, but I've looked over much of this stuff front-to-back.