mppt vs pwm

O.K., I think it's becoming more clear to me. The mppt is a matter of "sweeping", or "tracking", or "searching", but the method used to actually "regulate" is the pwm itself? And it's an "on/off" thing, that manipulates voltage by regulating spurts of current?

But then there is also the bucker. Does it make up for what pwm cannot do on it's own, because of too large a spread between voltages?