The POT adjusts Vout. The resistor under the amp meter represents the load; if you change the resistance (load) the OpAmp will maintain the desired Vout (until the OpAmp maxes output at 14V). For some reason this app is a bit glitchy with this circuit. Otherwise, in the real world I would use a step down transformer (actual power coming from the wall) to step down power and a BJT or MOSFET to control power to Vout; the transister base being controlled by the op amp output.
