Using the op-amp with little or no feedback so it's gain is very high will make the output swing from minimum to maximum (or the other way around if inverting) when the input voltages are the same or one exceeds the other. The idea is to put the sawtooth signal on one input and a DC voltage on the other. When the sawtooth voltage is less than the DC, the output is in one state, when it exceeds it the output state changes. By adjusting the DC (the 'threshold') you can set at which part of the sawtooth the effect occurs. A low DC voltage will make the output switch at the bottom of the sawtooth and as it is increased, it will switch nearer the peaks.
It's a system used frequently to change analog signals to digital in some amplifiers and ADC units. The 741 is a poor choice of op-amp, there are many comparator ICs which will work better, they have a more defines switching point and faster output change.
Brian.