Hi I would like to know how the circuit in the attached picture works.

I don't get it.

Thank you very much

 

Hello,

Are you sure that it is connected correctly?
Take a look at this page how it probably should be:
http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/square.html

Bertus

 

That circuit is a poor design, as there is too much hysteresis feedback.

I've re-drawn the schematic so that it is easier to understand, corrected the hysteresis, and added plots of the +, -, and output so that you can see how it works.

[eta]
The circuit that Bertus linked to uses a dual supply for the opamp, so the resistor divider like I used (R2, R4) can be simplified by removing R2.