The JFET (Q10) acts like a resistor/constant current source and feeds the Darlington transistor (Q14) and the zener diode (D22).

The zener diode will be rated for a certain voltage and that together with the constant current source will essentially lock it to that voltage.

The NPN transistors inside of Q14 will have a ~0,6-0,7V drop between the base (middle pin) and emitter (pin with the arrow), and since there's two set in series you'll have double that, but you also get to multiply the current gain (called Beta/hFE) of each transistor. If you can supply enough current to the transistor will be in saturation (they will have here) and then the only rule you'll have to follow is the one about voltage drops between the base and emitter, which will make it so that the voltage at the output of the regulator is zener voltage minus 2xVbe (1,2-1,4V)