When you do a voltage to current conversion circuit the output is current. Typically this signal (let's say 4 to 20 mA) is passed to a data logger. Most data loggers have a voltage input, however, for those designed for a current input the input resistance is low like either 250 or 500 ohms. This results in an actual voltage input of 1 to 5 or 2 to 10 volts. So when you look at the circuit and see Rl or Rload or load that is the actual input to the data logger and not a circuit component.
In the circuit you posted the first op amp is just a buffer but allows an offset adjust. The first op amp has a unity gain of 1 so Vin = Vout. If Vin were shorted to ground then the 20K offset pot would be adjusted for 0 Volts out of the first op amp. The second op amp serves as the current source driving the mosfet. If I have time later I might be able to put it together in a simulation. Just a tad busy right now.
Ron