This circuit uses a positive-feedback loop closed around~a combined comparator and integrator. When power is applied, the output of the comparator will switch to one of two states, to the maximum positive or maximum negative voltage. This applies a peak input signal to the integrator, and the integrator output will ramp either down or up, opposit` of the input signal. When the integrator output, which is connected to the comparator input, reaches a threshold sefby R1 and R2, the comparator will switch to the opposite polarity.
This cycle will repeat endlessly, the integrator charging positive then negative, and the comparator switching in a square-wave fashion.