Fuel valve

[Jam24]

I have a 2000 Suzuki 250 GZ and I'm new to riding. Unfortunately, I don't have the manual. I noticed the fuel value switch on my bike seems to have 4 settings (I'm including the positions as they would appear on a clock):

On (at 6 o'clock)
Off (at 9)
Fuel (at 5)
Res (at 12)
IMG_1410.jpg

What should I use each of these settings for?

Searching around online, I'm seeing a lot of references to "PRI", but I don't seem to have this.

Any suggestions would be very helpful!