Shake to start! Assuming that the output voltage starts off high, the voltage at the + pin is half the output voltage. The capacitor slowly charges up to the output voltage (the charging time depends on R and C), but as soon at the voltage at - slightly exceeds the voltage at + pin, the output swings low and a negative voltage appears at the + pin. The capacitor now charges into the negative until the voltage at - pin goes slightly below the voltage at the + pin, and the output swings high. The cycle continues. The waveform at the - pin is a sawtooth wave and the voltages at + pin and out are square waves. The output has two states, neither of which are stable and the circuit oscillates between the two states. The oscillation frequency depends on the RC time constant and the voltage divider.
