I'm trying to do
While using the makershield's potentiometer. How do I hook it up?
I would just use jumper cables to the LCD on the clear breadboard that came with the kit. (if that's what you have) Just solder a header strip to the LCD and then add the pots middle lead to pin 3 of the screen. If the LCD itself isn't wired, begin adding jumpers across from pin 1 and 5(LCD) to a GND (arduino), pin 2 (LCD) to a 5 volt output (arduino), pin 4 (LCD) to pin 12 (arduino), pin 6 (LCD) to pin 11, pin 11(LCD) to pin 5 (arduino), pin 12 (LCD) to pin 4 (arduino), pin 13 (LCD) to pin 3 (arduino), and pin 14 (LCD) to pin 2 (arduino). Then load up the "HelloWorld" file and begin testing it. If you can't see anything, turn the pot until you can see it clearly. Hopefully this is what you asked for.
look at this pic: http://a248.e.akamai.net/origin-cdn.volusion.com/aes3n.okhn2/v/vspfiles/photos/MSMS01-4.jpg?1319644269
at the bottom left(ish) there is a four pin header, one of these pins is POT, connect this to the LCD VO pin