I feel kind of silly about asking this, but I'm gonna have to. My '00 Savage doesn't have an "off" for the fuel on the petsmock, only ON, RESERVE, and the other one that's PRI or something...so which do I turn it to when I pull the bike into the garage? Instead of turning it to "off", am I supposed to turn it to RES?

If you look closely at the petcock, there is a vacuum hose running to the carb. When the engine is running, the vacuum pulls on a diaphram in the petcock that allows the fuel to flow. No vacuum, no flow.  

You can think of it as a petcock that turns itself off.

I thought "RES" was a reservoir of gas. Like when you go out of gas, then you turn it to "RES", It starts again with enough fuel till your next gas station. At least thats what I use it for.

Yup, I always thought of it as "reserve" fuel but "reservoir" fits too.  It's basically tapped at a lower level.  In any case, the vacuum petc0ck is a nice thing in my opinion.  When I got the Amal carb, I had the option of either converting the petc0ck to a manual version or installing a port for vacuum on the carb.  I chose the latter and am pleased with it so far.