There are 3 things that the gas switch can be turned to the read "Res", "Pri", and "On". I am assuming that On is obviously on and the Res is reserve, but does Pri mean prime? And what is the difference between "On" and "Pri" if it does stand for prime?

the petcocks are vacuum actuated so when youre "ON" it actually means that gas will flow when a vacuum is put to the petcock (the motor running).  The reserve also runs off vacuum but at a lower point in the tank. Prime flows freely without vacuum.

CableKid,

Congrats on your first post.  That "Gas Switch" is known as a petcock.  Here is a link that will answer your question.

http://wiki.gstwins.com/index.php?n=Upgrades.Petcock

- Porkchop

Normally leave it 'on', when it runs out of fuel use 'res', both only flow when the motor is running. If you need to get fuel to the carbs when they're empty, you need 'pri'. This is if you run out of fuel and don't switch to 'res' before the motor actually stops, if you have drained the carbs for some reason or left it sitting so long the fuel in the carbs has evaporated.
If you leave it on 'pri' when its stopped, there's a chance fuel might drain into your airbox if the carb needle/seats are worn. Sometimes there are issues with the vacuum system that turns the tap on and off (when its on 'on') and you might need to use 'pri' to get you home.
Hope that helps.

ok thanks guys sorry if it was a bother but this is my first bike and im just kind of nervous about not wrecking or ruining it hahaha

Maybe a sign I need to grow up- I still snicker every time I flip the switch and think of its official name.